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Smoothly deprecate and redirect Python functions/classes with smart warnings and auto-routing—keep your codebase clean while maintaining backward compatibility

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# pyDeprecate

**Deprecate Python APIs without breaking existing callers.**

Use pyDeprecate when you renamed a function, moved a class, or retired an argument but still need old user code to work during the migration window. A single decorator can emit a clear warning, forward the call to the new implementation, remap old argument names, and expose metadata that CI audit tools can enforce when the removal deadline arrives.

**Core capabilities:**

- **Warn and forward** deprecated functions or methods to replacements.
- **Rename or drop arguments** while preserving compatibility for old call sites.
- **Wrap classes, Enums, dataclasses, constants, and objects** with transparent deprecation proxies.
- **Audit deprecations in CI** so expired wrappers and deprecation chains do not quietly linger.

> **Author:** [Jiri Borovec](https://github.com/Borda) · **License:** Apache 2.0 · **Python:** 3.9+ · **Import:** `from deprecate import deprecated, deprecated_class` · **Docs:** https://borda.github.io/pyDeprecate/

______________________________________________________________________

<details>
 <summary>📋 Table of Contents</summary>

- [📖 Overview](#overview)
- [✨ Features](#features)
- [💾 Installation](#installation)
- [🚀 Quick Start](#quick-start)
- [🗺 API at a Glance](#api-at-a-glance)
- [📊 Comparison with Other Tools](#comparison-with-other-tools)
- [📚 Use-cases and Applications](#use-cases-and-applications)
  - [Simple function forwarding](#simple-function-forwarding)
  - [Advanced target argument mapping](#advanced-target-argument-mapping)
  - [Deprecation warning only](#deprecation-warning-only)
  - [Rename arguments within one function](#rename-arguments-within-one-function)
  - [Stacked deprecation decorators](#stacked-deprecation-decorators)
  - [Conditional skip](#conditional-skip)
  - [Class deprecation](#class-deprecation)
  - [Deprecating constants and instances](#deprecating-constants-and-instances)
  - [Deprecating Enums and dataclasses](#deprecating-enums-and-dataclasses)
  - [Automatic docstring updates](#automatic-docstring-updates)
  - [Injecting new required arguments](#injecting-new-required-arguments)
  - [Async functions](#async-functions)
- [🔇 Understanding the void() Helper](#understanding-the-void-helper)
- [🔍 Audit](#audit)
  - [Validating Wrapper Configuration](#validating-wrapper-configuration)
  - [Generating Deprecation Tables](#generating-deprecation-tables)
  - [Enforcing Deprecation Removal Deadlines](#enforcing-deprecation-removal-deadlines)
  - [Detecting Deprecation Chains](#detecting-deprecation-chains)
- [🧪 Testing Deprecated Code](#testing-deprecated-code)
- [🔧 Troubleshooting](#troubleshooting)
- [🤝 Contributing](#contributing)

</details>

## 📖 Overview

The common case is moving functionality across modules, packages, or public API names without breaking callers immediately. You keep the old entry point temporarily, show users what changed, and forward them to the replacement until the old name can be removed.

pyDeprecate also avoids warning spam: each deprecated function or class warns once by default, and you can route messages through Python warnings, logging, or any custom stream.

```bash
pip install pyDeprecate
```

[![PyPI - Python Version](https://img.shields.io/pypi/pyversions/pyDeprecate)](https://pypi.org/project/pyDeprecate/) [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://github.com/Borda/pyDeprecate/blob/main/LICENSE) [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2FBorda%2FpyDeprecate.svg?type=shield&issueType=license)](https://app.fossa.com/projects/git%2Bgithub.com%2FBorda%2FpyDeprecate?ref=badge_shield&issueType=license)

[![PyPI Status](https://badge.fury.io/py/pyDeprecate.svg)](https://badge.fury.io/py/pyDeprecate) [![PyPI Status](https://pepy.tech/badge/pyDeprecate)](https://pepy.tech/project/pyDeprecate) [![Conda](https://img.shields.io/conda/v/conda-forge/pyDeprecate?label=conda&color=success)](https://anaconda.org/conda-forge/pyDeprecate) ![Conda](https://img.shields.io/conda/dn/conda-forge/pyDeprecate?color=blue) [![CodeFactor](https://www.codefactor.io/repository/github/borda/pydeprecate/badge)](https://www.codefactor.io/repository/github/borda/pydeprecate) [![Documentation](https://img.shields.io/badge/docs-borda.github.io-blue)](https://borda.github.io/pyDeprecate/)

[![CI testing](https://github.com/Borda/pyDeprecate/actions/workflows/ci_testing.yml/badge.svg?branch=main&event=push)](https://github.com/Borda/pyDeprecate/actions/workflows/ci_testing.yml) [![Install pkg](https://github.com/Borda/pyDeprecate/actions/workflows/ci_install-pkg.yml/badge.svg?branch=main&event=push)](https://github.com/Borda/pyDeprecate/actions/workflows/ci_install-pkg.yml) [![codecov](https://codecov.io/gh/Borda/pyDeprecate/branch/main/graph/badge.svg?token=BG7RQ86UJA)](https://codecov.io/gh/Borda/pyDeprecate) [![pre-commit.ci status](https://results.pre-commit.ci/badge/github/Borda/pyDeprecate/main.svg)](https://results.pre-commit.ci/latest/github/Borda/pyDeprecate/main)

> **Read:** [Mastering API Deprecation in Python — the pain points and how pyDeprecate can help](https://medium.com/codex/mastering-api-deprecation-in-python-the-pain-points-and-how-pydeprecate-can-help-1dbfd90e2b62) — CodeX / Medium

## ✨ Features

- ⚠️ Deprecation warnings are shown once per function by default (prevents log spam)
- 🔄 Arguments are automatically mapped to the target function
- 🚫 The deprecated function body is never executed when using `target`
- ⚡ Minimal runtime overhead with zero dependencies (Python standard library only)
- 🛠️ Supports deprecating callables: functions, methods, class constructors, **generator functions** (`def gen(): yield` — warning fires eagerly at call time, before iteration begins), and **`async def` coroutine functions** (wrapper is `async def`, `inspect.iscoroutinefunction(wrapper)` returns `True`; warning fires when the coroutine is awaited)
- 🏠 Supports deprecating `@property` — all three accessors (`fget`, `fset`, `fdel`) fire `FutureWarning`; chain-style `.setter()` / `.deleter()` rebinding preserved via `_DeprecatedProperty` subclass. Also supports `@cached_property` (getter-only — no `fset`/`fdel`).
- 📦 Supports deprecating classes, Enums, dataclasses, and module-level constants/objects via transparent proxies (`deprecated_class` for types; `deprecated_instance` for objects, with optional read-only enforcement — blocks standard collection mutators: `append`, `pop`, `update`, `clear`, etc.; custom mutator names bypass this guard)
- 📝 Optionally, docstrings can be updated automatically in RST/Sphinx or MkDocs/Markdown format (auto-detected); ships bundled Griffe and Sphinx doc-engine extensions
- 🔍 Preserves original function signature, annotations and metadata for introspection
- ⚙️ Configurable warning message template and output stream (logging, warnings, custom callable)
- 🎯 Fine‑grained control: per‑argument deprecation/mapping, `args_extra` for injecting fixed forwarded kwargs, and conditional `skip_if` behavior
- 🧪 Includes testing helpers (e.g., `assert_no_warnings`, formerly `no_warning_call`) for deterministic tests
- 🔎 Audit tools for CI pipelines: validate wrapper config, enforce removal deadlines, and detect deprecated-to-deprecated chains

## 💾 Installation

Requires **Python 3.9 or later**.

Choose the install that matches the workflow you need:

| Workflow                     | Command                                | Includes                                                                                                      |
| ---------------------------- | -------------------------------------- | ------------------------------------------------------------------------------------------------------------- |
| Runtime deprecation wrappers | `pip install pyDeprecate`              | `@deprecated`, `@deprecated_class`, `deprecated_instance`, docstring helpers, and most audit metadata helpers |
| CI deadline checks           | `pip install 'pyDeprecate[audit]'`     | Adds `packaging` for PEP 440 version comparison in `validate_deprecation_expiry()`                            |
| Command-line audit workflows | `pip install 'pyDeprecate[audit,cli]'` | Adds CLI dependencies (`fire`, `rich`) plus expiry support for `pydeprecate expiry` and `pydeprecate all`     |

Base installation from PyPI:

```bash
pip install pyDeprecate
```

<details>
 <summary>Other installations</summary>

Simply install with pip from source:

```bash
pip install https://github.com/Borda/pyDeprecate/archive/main.zip
```

</details>

## 🚀 Quick Start

Here's the simplest way to get started with deprecating a function:

```python
from deprecate import deprecated

# NEW/FUTURE API — renamed to be more explicit about what it computes
def compute_sum(a: int = 0, b: int = 3) -> int:
    return a + b

# DEPRECATED API — `addition` was the original name before the rename
@deprecated(target=compute_sum, deprecated_in="1.0", remove_in="2.0")
def addition(a: int, b: int = 5) -> int:
    pass  # body is not needed — calls are forwarded to compute_sum

# Using the original name still works but shows a warning
result = addition(1, 2)  # Returns 3
# Warning: The `addition` was deprecated since v1.0 in favor of `__main__.compute_sum`.
#          It will be removed in v2.0.
print(result)
```

<details>
 <summary>Output: <code>addition(1, 2)</code></summary>

```
3
```

</details>

That's it! All calls to `addition()` are automatically forwarded to `compute_sum()` with a deprecation warning.

> [!IMPORTANT]
>
> When `target=<callable>` is set, pyDeprecate intercepts the call **before** the body executes — the body is dead code under normal forwarding. **Exception**: if `skip_if` evaluates `True` at call time, the source body runs as the fallback, so keep a working implementation when combining `target=<callable>` with `skip_if`.

## 🗺 API at a Glance

Not sure which API to reach for? Start here.

**Pick the right decorator:**

| Scenario                                      | API to use                                                               |
| --------------------------------------------- | ------------------------------------------------------------------------ |
| Renaming a function or method                 | `@deprecated(target=new_func)`                                           |
| Renaming an argument within the same function | `@deprecated(target=TargetMode.ARGS_REMAP, args_mapping={"old": "new"})` |
| Warn only — original body still runs          | `@deprecated(deprecated_in="1.0", remove_in="2.0")`                      |
| Deprecating a class, Enum, or dataclass name  | `@deprecated_class(target=NewClass)`                                     |
| Deprecating a module-level constant or object | `deprecated_instance(obj, ...)`                                          |

> **Note:** Legacy `target=None` and `target=True` emit `FutureWarning` at decoration time in v0.8 and become `TypeError` in v1.0. Use `TargetMode.NOTIFY` and `TargetMode.ARGS_REMAP` respectively.

<details>
 <summary>All `@deprecated` parameters at a glance:</summary>

| Param              | Default                     | Purpose                                                                                                                                                                 |
| ------------------ | --------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `target`           | `TargetMode.AUTO`           | `Callable` to forward to · `TargetMode.ARGS_REMAP` to remap args · `TargetMode.NOTIFY` warn-only · `TargetMode.AUTO` (default) infers the mode from the other arguments |
| `deprecated_in`    | `""`                        | Version when deprecated (e.g. `"1.0"`)                                                                                                                                  |
| `remove_in`        | `""`                        | Version when removed (e.g. `"2.0"`)                                                                                                                                     |
|                    | **Advanced: ~10% of cases** |                                                                                                                                                                         |
| `stream`           | `deprecation_warning`       | Warning sink callable (set `None` to silence warnings)                                                                                                                  |
| `num_warns`        | `1`                         | `0` never · `1` once · `-1` always · `N` exactly N times                                                                                                                |
| `args_mapping`     | `None`                      | `{"old": "new"}` rename · `{"old": None}` drop                                                                                                                          |
| `message_template` | `None`                      | Custom warning message template (`%`-style placeholders)                                                                                                                |
| `args_extra`       | `None`                      | Fixed kwargs injected into the target call                                                                                                                              |
| `skip_if`          | `False`                     | `bool` or `Callable → bool`; deactivate the deprecation machinery when true                                                                                             |
| `update_docstring` | `False`                     | Append Sphinx `.. deprecated::` notice to docstring                                                                                                                     |
| `docstring_style`  | `"auto"`                    | Docstring notice format: `auto` · `rst` · `mkdocs`/`markdown`                                                                                                           |

> [!TIP]
>
> All three decorators share every parameter above. The only differences: `deprecated_class()` adds the class-only `attrs_mapping` (attribute-name remapping — `TypeError` on the other two), and a **class source** is dispatched to `deprecated_class` by `@deprecated` but rejected with `TypeError` by `deprecated_callable()`. `TargetMode.AUTO` is front-door-only: `deprecated_callable()` defaults `target` to `TargetMode.NOTIFY`, `deprecated_class()` leaves it unset, and both raise `TypeError` when handed `TargetMode.AUTO` explicitly. `deprecated_instance()` shares `deprecated_in`, `remove_in`, `num_warns`, `stream`, `args_extra`, `message_template`, and `skip_if`; it requires `obj` and adds `name` (display name) and `read_only`.

</details>

## 📊 Comparison with Other Tools

> 💬 _How does pyDeprecate compare to other Python deprecation solutions?_

Most alternatives emit a deprecation notice. pyDeprecate is for migrations where the old API must keep working: it can forward calls, remap arguments, wrap class/object aliases, and audit removal deadlines.

- [`warnings.warn`](https://docs.python.org/3/library/warnings.html) (stdlib): the lowest-friction option for simple internal warnings.
- [`deprecation`](https://pypi.org/project/deprecation/) (Lib): a widely used library by Brian Curtin with version-based deprecation helpers.
- [`Deprecated`](https://pypi.org/project/Deprecated/) (wrapt): a decorator-based library by Laurent Laporte with `wrapt` integration.

<details>
 <summary>Key Advantages & Feature Breakdown</summary>

- **Simple Warnings**: Emits standard Python warnings, compatible with default error handling tools.
- **Auto-Forward Calls**: Automatically redirects calls to the new function, ensuring the deprecated code is *never* executed.
- **Generator / Async**: Works natively with generator functions (`def fn(): yield`), `async def` coroutines, and async generators (`async def fn(): yield`) — the deprecation warning fires at call time regardless of callable type, and the wrapper preserves the correct introspection flags (`iscoroutinefunction`, etc.).
- **Argument Mapping**: Seamlessly translates old API arguments to new ones, handling complex renames and restructuring.
- **Argument Deprecation**: Warns when specific arguments are used, even if the function itself isn't deprecated.
- **Docstring Updates**: Automatically appends deprecation notices to the function's docstring.
- **Version Tracking**: Clearly specifies `deprecated_in` and `remove_in` versions for better lifecycle management.
- **Prevent Log Spam**: Prevents log spam by showing warnings only once per function (or N times) by default.
- **Zero Extra Depend.**: Lightweight and easy to install, relying solely on the Python standard library.
- **Custom Streams**: Route warnings to `logging`, standard `warnings`, or any custom callable to fit your monitoring stack.
- **Testing Helpers**: Built-in tools like `assert_no_warnings()` ensure your deprecations are testable and deterministic.
- **Class/Instance Proxy**: Deprecate entire classes, Enums, dataclasses, and module-level objects with transparent proxy wrappers (`deprecated_class`, `deprecated_instance`).
- **CI/Audit Tools**: Validate wrapper configuration, and — when installed with the `pyDeprecate[audit]` extra — enforce removal deadlines (PEP 440) and detect deprecated-to-deprecated chains.
- **Static Type-Checker Signals**: Native PEP 702 static diagnostics come from `warnings.deprecated`. For projects that need both static-checker hints and runtime call-forwarding, `warnings.deprecated` (for the static signal) and pyDeprecate's `@deprecated` (for forwarding) can be applied separately to the same function.
- **Decorator Stacking**: Stack `@deprecated` decorators for multi-version migrations — rename arguments across releases (`ARGS_REMAP + ARGS_REMAP`), then deprecate the whole function when a complete replacement arrives (`ARGS_REMAP + NOTIFY`). Unsupported combinations warn at decoration time.
- **Sphinx Plugin**: Ships a Sphinx autodoc extension (`deprecate.docstring.sphinx_ext`) so `_DeprecatedProxy` objects are documented with their injected deprecation notice instead of rendering as opaque aliases.
- **MkDocs Plugin**: Ships a Griffe extension (`deprecate.docstring.griffe_ext`) for mkdocstrings so runtime-injected `!!! warning` admonitions are visible in MkDocs-generated API docs.

</details>

> **When to prefer `warnings.deprecated` (PEP 702):** If your project targets Python 3.13+ and you only need simple call-site warnings visible to static type-checkers (mypy, pyright, IDEs), the stdlib decorator is the right choice — zero extra dependency. `warnings.warn` tells users what is deprecated; pyDeprecate tells users what to use instead and does the forwarding for them. Choose `pyDeprecate` when you need call-forwarding, argument remapping, proxy wrapping of module-level constants, or CI audit tools — none of those exist in PEP 702. On Python < 3.13, `typing_extensions.deprecated` requires `typing_extensions` (marked ✍️ for that reason).

| _Feature_                 | `pyDeprecate` | `warnings.warn` (stdlib) | `deprecation` (Lib) | `Deprecated` (wrapt) | `warnings.deprecated`† (py3.13+) |
| ------------------------- | :-----------: | :----------------------: | :-----------------: | :------------------: | :------------------------------: |
| **Simple Warnings**       |      ✅       |            ✅            |         ✅          |          ✅          |                ✅                |
| **Auto-Forward Calls**    |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **Generator / Async**     |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **Argument Mapping**      |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **Argument Deprecation**  |      ✅       |            ✍️            |         ❌          |          ❌          |                ❌                |
| **Class/Instance Proxy**  |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **Docstring Updates**     |      ✅       |            ❌            |         ✅          |          ✅          |                ❌                |
| **Version Tracking**      |      ✅       |            ✍️            |         ✅          |          ✅          |                ❌                |
| **Prevent Log Spam**      |      ✅       |            ✍️            |         ❌          |          ❌          |                ❌                |
| **Zero Extra Depend.**    |      ✅       |            ✅            |         ❌          |          ❌          |                †                 |
| **Custom Streams**        |      ✅       |            ✍️            |         ❌          |          ❌          |                ❌                |
| **Testing Helpers**       |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **CI/Audit Tools**        |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **Static Checker Signal** |      ✍️       |            ❌            |         ❌          |          ❌          |                ✅                |
| **Decorator Stacking**    |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **Sphinx Plugin**         |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |
| **MkDocs Plugin**         |      ✅       |            ❌            |         ❌          |          ❌          |                ❌                |

✍️ = possible but requires manual implementation † `warnings.deprecated` in the stdlib on Python 3.13+ (PEP 702); also available as `typing_extensions.deprecated` for Python < 3.13

_This positioning guide is not a full cell-by-cell external audit and may drift from upstream tools over time; [open an issue](https://github.com/Borda/pyDeprecate/issues) if you spot an inaccuracy._

**Fair strengths in alternative tools worth considering:**

- `warnings.deprecated` is the best option when your top priority is IDE/type-checker diagnostics with no runtime behavior changes; it also adds no per-call runtime overhead when the warning category is suppressed.
- `deprecation` includes `@fail_if_not_removed`, a focused test helper for direct test-failure enforcement when removal deadlines are reached.
- `Deprecated` — `deprecated.sphinx` includes `@versionadded` and `@versionchanged` decorators that inject Sphinx directives into docstrings for lifecycle annotation in Sphinx-built API docs.
- `warnings.warn` stays the lowest-friction option for one-off internal warnings where compatibility shims are unnecessary.

> [!NOTE]
>
> This comparison is compiled to the best of our knowledge and we're happy to make any justified corrections. If you spot an inaccuracy, please [open an issue](https://github.com/Borda/pyDeprecate/issues) or submit a PR.

> [!TIP]
>
> Every deprecation variant writes the same `DeprecationConfig` — `@deprecated`, `deprecated_class`, `deprecated_instance`, and the audit tools all read from a single source of truth. This means your CI pipeline (`pydeprecate check src/`) catches misconfigured wrappers across all three variants with one scan.

## 📚 Use-cases and Applications

The functionality is kept simple and all defaults should be reasonable, but you can still do extra customization such as:

- 💬 define user warning message and preferred stream
- 🔀 extended argument mapping to target function/method
- 🎯 define deprecation logic for renamed arguments within one function
- 📊 specify warning count per:
  - called function (for func deprecation)
  - used arguments (for argument deprecation)
- ⚙️ define conditional skip (e.g. depending on some package version)

In particular the target values (cases):

| `target` value | Use case | `args_mapping` | Warning trigger |
| --------------------------- | ----------------------------------------------------------------------- | --------------------------------------------------------- | ---------------------------------- |
| `TargetMode.NOTIFY` | Whole callable going away; no replacement yet | Ignored (warns; TypeError in v1.0) | Every call |
| `TargetMode.ARGS_REMAP` | Callable stays; argument names are renamed | Required | Only when old arg names are passed |
| `<callable>` | Callable replaced by another; calls forwarded | Optional | Every call |
| `TargetMode.AUTO` (default) | Fallback for an **omitted** `target` — mode inferred at decoration time | Presence resolves `ARGS_REMAP`; absence resolves `NOTIFY` | Follows the resolved mode |

> [!TIP]
>
> **Prefer passing an explicit `target`** — one of the first three rows — so the intent is visible at the call site. `TargetMode.AUTO` is only the default that resolves an omitted `target`; you never write `target=TargetMode.AUTO` yourself, and the strict `deprecated_callable()` / `deprecated_class()` forms reject it. `TargetMode.NOTIFY` replaces the old `target=None` sentinel and `TargetMode.ARGS_REMAP` replaces the old `target=True` sentinel; the old forms still work but emit a `FutureWarning` at decoration time.

> [!NOTE]
>
> `@deprecated` is primarily for functions and methods. Applied to a class it also works — it dispatches to `@deprecated_class()` (a permanent, supported path) and emits a one-time informational `UserWarning` (only this notice is removed, in v1.0; suppressed by `stream=None`) — but prefer `@deprecated_class()` directly for classes, Enums, and dataclasses (see [Deprecating Enums and dataclasses](#deprecating-enums-and-dataclasses)): same result, no notice, and it exposes class-only options such as `attrs_mapping`. If you want a strict callable-only form that refuses a class up front instead, use `@deprecated_callable()` — it shares every parameter with `@deprecated` and raises `TypeError` at decoration time when applied to a class.

### ➡ Simple function forwarding

It is very straightforward: you forward your function call to a new function and all arguments are mapped:

```python
# NEW/FUTURE API — renamed to be more explicit about what it computes
def compute(a: int = 0, b: int = 3) -> int:
    """New function anywhere in the codebase or even other package."""
    return a + b

# ---------------------------

from deprecate import deprecated

# What this module looked like before the rename:
# def calculate(a: int, b: int = 5) -> int:
#     return a + b

# DEPRECATED API — `calculate` was the original name before the rename
@deprecated(target=compute, deprecated_in="0.1", remove_in="0.5")
def calculate(a: int, b: int = 5) -> int:
    """
    My deprecated function which now has an empty body
     as all calls are routed to the new function.
    """
    pass  # or you can just place docstring as one above

# calling this function will raise a deprecation warning:
#   The `calculate` was deprecated since v0.1 in favor of `__main__.compute`.
#   It will be removed in v0.5.
print(calculate(1, 2))
```

<details>
 <summary>Output: <code>calculate(1, 2)</code></summary>

```
3
```

</details>

<details>
<summary>Wrapper form: applying <code>@deprecated</code> without the decorator syntax</summary>

When the deprecated name already exists as a callable (for example, imported from another package), you can apply `deprecated()` directly without redefining the function:

```python
from deprecate import deprecated

# NEW/FUTURE API — in real usage this would be imported from another module
def compute_sum(a: int, b: int = 0) -> int:
    return a + b

# LEGACY — already-existing callable that is being deprecated
def addition(a: int, b: int = 0) -> int:
    return a + b

# DEPRECATED API — `calculate` was the original name in this package;
# wrap it without redefining a function body
calculate = deprecated(
    target=compute_sum,
    deprecated_in="0.5",
    remove_in="1.0",
)(addition)
print(calculate(1, 2))
```

<details>
 <summary>Output: <code>calculate(1, 2)</code></summary>

```
3
```

</details>

This is an equivalent to the `@deprecated(...)` decorator form but applied to an already-existing callable — useful when the deprecated function lives in a dependency you don't control.

</details>

### 🔀 Advanced target argument mapping

Use argument mapping when the replacement function keeps the same meaning but uses different parameter names:

<details>
 <summary>Example: mapping deprecated args to <code>sklearn.metrics.accuracy_score</code></summary>

```python
import logging
from sklearn.metrics import accuracy_score
from deprecate import deprecated, void

@deprecated(
    # use standard sklearn accuracy implementation
    target=accuracy_score,
    # custom warning stream
    stream=logging.warning,
    # number of warnings per lifetime (with -1 for always)
    num_warns=5,
    # lifecycle metadata shown in the deprecation notice and audit output
    deprecated_in="0.6",
    remove_in="1.0",
    # custom message template
    message_template="`%(source_name)s` was deprecated, use `%(target_path)s`",
    # as target args are different, define mapping from source to target func
    args_mapping={"preds": "y_pred", "target": "y_true", "blabla": None},
)
def depr_accuracy(preds: list, target: list, blabla: float) -> float:
    """My deprecated function which is mapping to sklearn accuracy."""
    # to stop complain your IDE about unused argument you can use void/empty function
    return void(preds, target, blabla)

# calling this function will raise a deprecation warning:
#   WARNING:root:`depr_accuracy` was deprecated, use `sklearn.metrics.accuracy_score`
print(depr_accuracy([1, 0, 1, 2], [0, 1, 1, 2], 1.23))
```

sample output:

```
0.5
```

</details>

### ⚠ Deprecation warning only

Base use-case with no forwarding and just raising a warning:

```python
from deprecate import deprecated

@deprecated(deprecated_in="0.1", remove_in="0.5")
def my_sum(a: int, b: int = 5) -> int:
    """My deprecated function which still has to have implementation."""
    return a + b

# calling this function will raise a deprecation warning:
#   The `my_sum` was deprecated since v0.1. It will be removed in v0.5.
print(my_sum(1, 2))
```

<details>
 <summary>Output: <code>my_sum(1, 2)</code></summary>

```
3
```

</details>

> [!NOTE]
>
> When using `TargetMode.NOTIFY`, the deprecated function's implementation must be preserved and will be executed. The deprecation decorator only adds a warning without forwarding.

### 🔄 Rename arguments within one function

Use `TargetMode.ARGS_REMAP` when the function stays in place but one of its arguments has been renamed or removed:

```python
from deprecate import TargetMode, deprecated

@deprecated(
    # rename an argument within the same function
    target=TargetMode.ARGS_REMAP,
    args_mapping={"coef": "new_coef"},
    # common version info
    deprecated_in="0.2",
    remove_in="0.4",
)
def any_pow(base: float, coef: float = 0, new_coef: float = 0) -> float:
    """My function with deprecated argument `coef` mapped to `new_coef`."""
    return base**new_coef

# calling this function will raise a deprecation warning:
#   The `any_pow` uses deprecated arguments: `coef` -> `new_coef`.
#   They were deprecated since v0.2 and will be removed in v0.4.
print(any_pow(2, 3))
```

<details>
 <summary>Output: <code>any_pow(2, 3)</code></summary>

```
8
```

</details>

To **drop** an argument entirely (warn when it's passed, then discard it), map it to `None`:

```python
from deprecate import TargetMode, deprecated
from typing import Optional

@deprecated(
    target=TargetMode.ARGS_REMAP,
    args_mapping={"legacy_param": None},
    deprecated_in="1.8",
    remove_in="1.9",
)
def my_func(value: int, legacy_param: Optional[str] = None) -> int:
    """legacy_param is no longer used; pass None or omit it."""
    return value * 2

# Passing the removed argument triggers a warning and the argument is silently discarded:
#   The `my_func` uses deprecated arguments: `legacy_param` -> `None`.
#   They were deprecated since v1.8 and will be removed in v1.9.
print(my_func(value=42, legacy_param="old"))
```

<details>
 <summary>Output: <code>my_func(value=42, legacy_param="old")</code></summary>

```
84
```

</details>

> [!WARNING]
>
> `TargetMode.ARGS_REMAP` without `args_mapping` is a misconfiguration; using it emits a construction-time `UserWarning`. This will become a `TypeError` in v1.0. If you only want to warn callers with no forwarding or remapping, use `TargetMode.NOTIFY` instead.

### 🔗 Stacked deprecation decorators

Stack `@deprecated` decorators to handle multi-version deprecation migrations. Each layer tracks its own version range and warning count independently.

<details>
 <summary>Pattern 1: multi-step argument renames (ARGS_REMAP + ARGS_REMAP)</summary>

```python
from deprecate import TargetMode, deprecated

@deprecated(
    target=TargetMode.ARGS_REMAP,
    deprecated_in="0.3",
    remove_in="0.6",
    args_mapping=dict(c1="nc1"),
    message_template="Depr: v%(deprecated_in)s rm v%(remove_in)s for args: %(argument_map)s.",
)
@deprecated(
    target=TargetMode.ARGS_REMAP,
    deprecated_in="0.4",
    remove_in="0.7",
    args_mapping=dict(nc1="nc2"),
    message_template="Depr: v%(deprecated_in)s rm v%(remove_in)s for args: %(argument_map)s.",
)
def any_pow(base, c1: float = 0, nc1: float = 0, nc2: float = 2) -> float:
    return base**nc2

# calling this function will raise deprecation warnings:
#   FutureWarning('Depr: v0.3 rm v0.6 for args: `c1` -> `nc1`.')
#   FutureWarning('Depr: v0.4 rm v0.7 for args: `nc1` -> `nc2`.')
print(any_pow(2, 3))
```

code output:

```
8
```

</details>

<details>
 <summary>Pattern 2: lifecycle migration (ARGS_REMAP + NOTIFY)</summary>

Rename an argument in v1.0, then deprecate the whole function in v2.0 when a complete replacement exists. `ARGS_REMAP` must be the outermost (top) decorator; `NOTIFY` goes below it.

```python
from deprecate import TargetMode, deprecated

@deprecated(TargetMode.ARGS_REMAP, deprecated_in="1.0", remove_in="2.0", args_mapping={"factor": "scale"})
@deprecated(TargetMode.NOTIFY, deprecated_in="2.0", remove_in="3.0")
def compute_power(base: float, factor: float = 1, scale: float = 1) -> float:
    return base**scale

print(compute_power(2, factor=3))  # → 2 warnings (arg rename + function deprecated)
print(compute_power(2, scale=3))  # → 1 warning  (function deprecated only)
```

</details>

<details>
 <summary>Output: <code>compute_power(2, factor=3); compute_power(2, scale=3)</code></summary>

```
8
8
```

</details>

| Outer (top) | Inner (bottom) | Status | Notes |
| ------------ | -------------- | ---------------------------------- | ----------------------------------------------------------------------- |
| `ARGS_REMAP` | `ARGS_REMAP` | ✓ Supported | Multi-step argument renames across versions |
| `ARGS_REMAP` | `NOTIFY` | ✓ Supported | Lifecycle: rename args first, then deprecate the whole function |
| `NOTIFY` | `callable` | ✓ Supported | Outer NOTIFY warns callers; inner callable handles forwarding |
| `callable` | `callable` | ✗ `UserWarning` at decoration time | Use a single `@deprecated(target=<callable>)` instead |
| `callable` | `ARGS_REMAP` | ✗ `UserWarning` at decoration time | Collapse to `@deprecated(target=fn, args_mapping={...})` |
| `callable` | `NOTIFY` | ✗ `UserWarning` at decoration time | Collapse to a single `@deprecated(target=<callable>)` |
| `ARGS_REMAP` | `callable` | ✗ `UserWarning` at decoration time | Update the inner decorator to include `target=` and `args_mapping=` |
| `NOTIFY` | `NOTIFY` | ✗ `UserWarning` at decoration time | Update the existing decorator's versions instead of adding a second one |
| `NOTIFY` | `ARGS_REMAP` | ✗ `UserWarning` at decoration time | Wrong order — swap: `ARGS_REMAP` on top, `NOTIFY` below |

### ⚙ Conditional skip

Use `skip_if` when the deprecation notice should depend on runtime state such as an installed package version. It is available on `@deprecated`, `deprecated_callable()`, `deprecated_class()`, and `deprecated_instance()`; on a class or instance proxy an active skip serves the wrapped source silently — no warning, no mapping, no target forwarding:

<details>
<summary>Example: <code>skip_if</code> based on a runtime condition</summary>

```python
from deprecate import TargetMode, deprecated_callable

FAKE_VERSION = 1

def version_greater_1():
    return FAKE_VERSION > 1

@deprecated_callable(
    target=TargetMode.ARGS_REMAP,
    deprecated_in="0.3",
    remove_in="0.6",
    args_mapping=dict(c1="nc1"),
    skip_if=version_greater_1,
)
def skip_pow(base, c1: float = 1, nc1: float = 1) -> float:
    return base ** (c1 - nc1)

# calling this function will raise a deprecation warning
print(skip_pow(2, 3))

# change the fake versions
FAKE_VERSION = 2

# will not raise any warning
print(skip_pow(2, 3))
```

</details>

<details>
 <summary>Output: <code>skip_pow(2, 3); skip_pow(2, 3)</code></summary>

```
0.25
4
```

</details>

This pattern is useful when a migration is only active for some environments or dependency versions.

### 🏗 Class deprecation

Two common patterns: deprecating a single method (rename within the same class) or deprecating the whole class by forwarding `__init__` to a successor.

<details>
<summary>Example: renaming a method within the same class</summary>

```python
from deprecate import deprecated, void

class MyService:
    # NEW/FUTURE API — renamed from run() for clarity
    def execute(self, x: int) -> int:
        """Current method."""
        return x * 2

# DEPRECATED API — `run` was the original name before the rename
    @deprecated(target=execute, deprecated_in="1.0", remove_in="2.0")
    def run(self, x: int) -> int:
        """Deprecated — renamed to execute()."""
        return void(x)

svc = MyService()
# calling this method will raise a deprecation warning:
#   The `run` was deprecated since v1.0 in favor of `__main__.execute`.
#   It will be removed in v2.0.
print(svc.run(5))
```

</details>

<details>
 <summary>Output: <code>svc.run(5)</code></summary>

```
10
```

</details>

<details>
<summary>Example: forwarding <code>__init__</code> to a successor class</summary>

```python
# NEW/FUTURE API — renamed to be more descriptive
class HttpClient:
    """My new class anywhere in the codebase or other package."""

def __init__(self, c: float, d: str = "abc"):
        self.my_c = c
        self.my_d = d

# ---------------------------

from deprecate import deprecated, void

# DEPRECATED API — `Client` was the original name before it was renamed to HttpClient
class Client(HttpClient):
    """
    The deprecated class should be inherited from the successor class
     to hold all methods and properties.
    """

@deprecated(target=HttpClient, deprecated_in="0.2", remove_in="0.4")
    def __init__(self, c: int, d: str = "efg"):
        """
        You place the decorator around __init__ as you want
         to warn user just at the time of creating object.

Decorating __init__ warns at instantiation time and optionally
        forwards to another class. For deprecating the class itself
        (name change, Enum, dataclass), use @deprecated_class() instead.
        """
        void(c, d)

# calling this function will raise a deprecation warning:
#   The `Client` was deprecated since v0.2 in favor of `__main__.HttpClient`.
#   It will be removed in v0.4.
inst = Client(7)
print(inst.my_c)  # returns: 7
print(inst.my_d)  # returns: "efg"
```

</details>

<details>
 <summary>Output: <code>inst.my_c; inst.my_d</code></summary>

```
7
efg
```

</details>

### 📦 Deprecating constants and instances

Use `deprecated_instance` to wrap module-level objects such as dicts, lists, constants, or custom objects with transparent deprecation warnings. Attribute, item, call, and common data-use operations forward to the wrapped object, while `isinstance` checks and structural introspection stay silent so type guards keep working.

The `name` parameter is optional; when omitted it defaults to the wrapped object's type name. Use `read_only=True` for shared constants or config objects that callers should not mutate through the deprecated alias. For operator, copy, pickle, and introspection edge cases, see [Classes → Constants and instances](https://borda.github.io/pyDeprecate/stable/guide/classes.html#constants-and-instances) and [Troubleshooting](https://borda.github.io/pyDeprecate/stable/troubleshooting.html#do-arithmetic-and-operator-protocol-methods-emit-deprecation-notices-on-deprecated_instance-proxies).

```python
from deprecate import deprecated_instance

# NEW/FUTURE API — renamed to be more explicit about its scope
TRAINING_CONFIG = {"lr": 0.001, "batch_size": 32, "epochs": 10}

# What it looked like before the rename:
# DEFAULTS = {"lr": 0.001, "batch_size": 32, "epochs": 10}

# DEPRECATED API — `DEFAULTS` was the original name; read-only so
# callers cannot mutate shared state through the deprecated alias
DEFAULTS = deprecated_instance(
    TRAINING_CONFIG,
    deprecated_in="1.2",
    remove_in="2.0",
    read_only=True,
)

# Reading still works but emits a FutureWarning once:
#   The `dict` was deprecated since v1.2. It will be removed in v2.0.
print(DEFAULTS["lr"])  # 0.001
```

<details>
 <summary>Output: <code>DEFAULTS["lr"]</code></summary>

```
0.001
```

</details>

### 🗂 Deprecating Enums and dataclasses

<details>
<summary>Example: <code>deprecated_class()</code> for Enum and dataclass</summary>

`deprecated_class()` wraps an entire Enum or dataclass in a transparent proxy that warns on every access and forwards attribute, item, and call operations to the replacement class. Use `args_mapping` to rename or drop kwargs when the deprecated class is called.

> [!NOTE]
>
> Type checks with `isinstance()` and `issubclass()` work transparently with `deprecated_class()` proxies and do not emit deprecation warnings, as these are structural checks rather than actual usage of the deprecated API.

```python
from enum import Enum
from dataclasses import dataclass
from deprecate import deprecated_class

# mypackage/theme.py — what it looked like before the rename:
#
# class Color(Enum):
#     RED = 1
#     BLUE = 2

# NEW/FUTURE API — renamed to be more descriptive
class ThemeColor(Enum):
    RED = 1
    BLUE = 2

# DEPRECATED API — `Color` was the original name; no class body needed,
# the proxy forwards all access to ThemeColor
Color = deprecated_class(target=ThemeColor, deprecated_in="1.0", remove_in="2.0")(ThemeColor)

# All access is forwarded to ThemeColor — a FutureWarning is emitted once:
#   The `Color` was deprecated since v1.0. It will be removed in v2.0.
print(Color.RED is ThemeColor.RED)  # True
print(Color(1) is ThemeColor.RED)  # True
print(Color["RED"] is ThemeColor.RED)  # True

# Precision migration story:
# - PointV1 used integer pixel coordinates.
# - PointV2 supports float coordinates for sub-pixel precision and smoother transforms.

# NEW/FUTURE API — extended to float precision
@dataclass
class PointV2:
    x: float
    y: float

# DEPRECATED API — PointV1 was the original integer-coordinate implementation
@deprecated_class(target=PointV2, deprecated_in="1.8", remove_in="2.0")
@dataclass
class PointV1:
    x: int
    y: int

# Existing callers using integer coordinates still work and are forwarded to PointV2:
p_old = PointV1(3, 4)
print(isinstance(p_old, PointV2))
print((p_old.x, p_old.y))

# New callers can use higher precision directly:
p_new = PointV2(3.25, 4.75)
print((p_new.x, p_new.y))
```

</details>

<details>
 <summary>Output: <code>Color.RED is ThemeColor.RED; Color(1) is ThemeColor.RED; (p_new.x, p_new.y)</code></summary>

```
True
True
True
True
(3, 4)
(3.25, 4.75)
```

</details>

<details>
<summary>Example: selective attribute deprecation with <code>attrs_mapping</code></summary>

Use `attrs_mapping` to deprecate only specific attribute names — other attributes pass through silently. Covers renames, misspelling corrections, warn-only notices, and Enum member aliases. Non-`None` mapping values must exist on the `target` class when `target=` is provided, or on the wrapped class otherwise. Entries mapped to `None` keep the same attribute name but still resolve on the active class, so `target=NewClass` with `attrs_mapping={"size": None}` warns and then reads, writes, or deletes `NewClass.size`. Non-cyclic chains are allowed at decoration time and reported by audit; cycles raise immediately.

**Decorator syntax** — apply `@deprecated_class(attrs_mapping=...)` at class definition time:

```python
from deprecate import deprecated_class

@deprecated_class(
    attrs_mapping={"color": "colour"},  # "color" is the deprecated spelling
    deprecated_in="2.0",
    remove_in="3.0",
)
class Palette:
    colour: str = "red"  # canonical name
    size: int = 10  # unlisted — passes through silently

print(Palette.color)  # warns: FutureWarning — redirected to colour → "red"
print(Palette.colour)  # silent
print(Palette.size)  # silent
```

<details>
 <summary>Output: <code>Palette.color; Palette.colour; Palette.size</code></summary>

```
red
red
10
```

</details>

**Wrapper form** — equivalent, useful when wrapping an existing class:

```python
from deprecate import deprecated_class

class Config:
    colour: str = "red"
    size: int = 42
    timeout: int = 30

# "color" → "colour" rename; "size" warn-only (None = no rename, just warn)
DeprecatedConfig = deprecated_class(
    attrs_mapping={"color": "colour", "size": None},
    deprecated_in="1.0",
    remove_in="2.0",
)(Config)

print(DeprecatedConfig.color)  # warns: FutureWarning — redirected to colour → "red"
print(DeprecatedConfig.colour)  # silent
print(DeprecatedConfig.timeout)  # silent
```

<details>
 <summary>Output: <code>DeprecatedConfig.color; DeprecatedConfig.colour; DeprecatedConfig.timeout</code></summary>

```
red
red
30
```

</details>

Each deprecated attribute name has its own independent warning counter — with `num_warns=1`, both `color` and `size` each emit one warning, not one shared across all entries. See [Selective attribute deprecation](https://borda.github.io/pyDeprecate/stable/guide/classes.html#selective-attribute-deprecation) in the docs for write/delete redirect and Enum member alias examples.

**Dataclass auto-expand** — when the wrapped class is a `@dataclass`, a single `deprecated_class(attrs_mapping={"old": "new"})` call automatically warns on both attribute access (`obj.old`) and constructor kwargs (`DC(old=5)`). No need to set `args_mapping` separately for a field rename. For non-`@dataclass` targets, `attrs_mapping` covers attribute access only — also set `args_mapping` to cover constructor kwargs.

**Explicit `TargetMode.ATTRS_REMAP` form** — passing `attrs_mapping` alone auto-resolves to `TargetMode.ATTRS_REMAP`. The equivalent self-documenting form is to pass `target=TargetMode.ATTRS_REMAP` together with `attrs_mapping`; both forms are behaviourally identical. Three misconfigurations emit `UserWarning` at decoration time (planned `TypeError` in v1.0): `target=TargetMode.ATTRS_REMAP` without `attrs_mapping` (no selective effect), `attrs_mapping={}` (empty dict), and explicit `target=TargetMode.NOTIFY` together with `attrs_mapping` — they contradict, so the proxy keeps `NOTIFY`, leaves the mapping inert at runtime, and records it in audit metadata with `misconfigured=True`; explicit configuration is never silently rewritten. Auto-resolve applies only when `target` is omitted. Using `@deprecated(target=TargetMode.ATTRS_REMAP)` raises `TypeError` for any source — function, property, **or class** — because the front door does not expose `attrs_mapping`; the mode is proxy-only, so reach for `deprecated_class(attrs_mapping=...)` directly.

To deprecate attributes at different library versions, stack two `@deprecated_class()` decorators — each layer carries its own version pair and `isinstance()`/`issubclass()` resolve correctly through the proxy chain.

</details>

### 📝 Automatic docstring updates

You can automatically inject deprecation information into your function's docstring:

<details>
<summary>Example: <code>update_docstring=True</code> inserts a Sphinx deprecation notice before <code>Args:</code>/<code>Parameters</code></summary>

```python
# NEW/FUTURE API — renamed to be more explicit about what it does
def transform(x: int) -> int:
    """New implementation of the function."""
    return x * 2

# ---------------------------

from deprecate import deprecated

# DEPRECATED API — `process` was the original name before the rename
@deprecated(
    target=transform,
    deprecated_in="1.0",
    remove_in="2.0",
    update_docstring=True,  # Enable automatic docstring updates
)
def process(x: int) -> int:
    """Transforms the input value.

Args:
        x: Input value

Returns:
        Result of computation
    """
    pass

# The docstring now includes deprecation information (inserted before "Args:")
print(process.__doc__)
# Output includes:
# .. deprecated:: 1.0
#    Will be removed in 2.0.
#    Use `__main__.transform` instead.
```

</details>

If you build docs with MkDocs/Markdown, you can switch to admonition output:

```python
from deprecate import deprecated

def transform(x: int) -> int:
    return x * 2

@deprecated(
    target=transform,
    deprecated_in="1.0",
    remove_in="2.0",
    update_docstring=True,
    docstring_style="mkdocs",  # alias: "markdown"
)
def process(x: int) -> int:
    """Transforms the input value."""
    pass

print(process.__doc__)
# !!! warning "Deprecated in 1.0"
#     Will be removed in 2.0.
#     Use `__main__.transform` instead.
```

This is useful for generating API docs with Sphinx, MkDocs, and strict Google/NumPy docstring parsers.

**MkDocs** (via `mkdocstrings` + Griffe extension):

![MkDocs demo — deprecation notice rendered as a warning admonition](https://raw.githubusercontent.com/Borda/pyDeprecate/main/docs/assets/images/demo-docs-mkdocs.png)

**Sphinx** (via `autodoc` + Sphinx extension):

![Sphinx demo — deprecation notice rendered as a styled deprecated directive](https://raw.githubusercontent.com/Borda/pyDeprecate/main/docs/assets/images/demo-docs-sphinx.png)

See the live rendered output in the online demos: [Sphinx demo](https://borda.github.io/pyDeprecate/stable/demo-sphinx/api.html) · [MkDocs demo](https://borda.github.io/pyDeprecate/stable/demo-mkdocs/api.html).

<details>
<summary>MkDocs integration: render injected notices with <code>mkdocstrings</code></summary>

`@deprecated(update_docstring=True)` modifies `fn.__doc__` at **import time**. [mkdocstrings](https://mkdocstrings.github.io/) uses [Griffe](https://mkdocstrings.github.io/griffe/) to read docstrings from the **source AST**, so it never sees that runtime change. To bridge the gap, pyDeprecate ships a Griffe extension:

```yaml
# mkdocs.yml
plugins:
  - mkdocstrings:
      handlers:
        python:
          extensions:
            - deprecate.docstring.griffe_ext:RuntimeDocstrings
```

With the extension registered, mkdocstrings will render the injected `!!! warning` admonition for every `@deprecated` function in your docs. No extra dependencies are required — `griffe` is already a dependency of `mkdocstrings[python]`.

</details>

### ➕ Injecting new required arguments

When the target function gains a new parameter that callers of the old API never passed, use `args_extra` to inject a fixed value at the wrapper level:

```python
from deprecate import deprecated, void

# NEW/FUTURE API — `send_email` adds an explicit `priority` field
def send_email(to: str, subject: str, priority: str) -> str:
    return f"Sent to {to!r}: {subject!r} [{priority}]"

# DEPRECATED API — `notify` was the original name; it had no `priority` concept
@deprecated(
    target=send_email,
    deprecated_in="1.5",
    remove_in="2.0",
    # callers of `notify` never passed `priority`, so inject a sensible default
    args_extra={"priority": "normal"},
)
def notify(to: str, subject: str) -> str:
    """Deprecated — use send_email() with an explicit priority instead."""
    return void(to, subject)

# calling this function will raise a deprecation warning:
#   The `notify` was deprecated since v1.5 in favor of `__main__.send_email`.
#   It will be removed in v2.0.
print(notify("alice@example.com", "Hello"))
```

<details>
 <summary>Output: <code>notify("alice@example.com", "Hello")</code></summary>

```
Sent to 'alice@example.com': 'Hello' [normal]
```

</details>

> [!NOTE]
>
> `args_extra` is merged into kwargs _after_ `args_mapping` is applied, so extra values can override mapped ones. It is used when `target` is a Callable or `TargetMode.ARGS_REMAP` (with `args_mapping`). For `TargetMode.NOTIFY`, it is ignored and a construction-time `UserWarning` is emitted by validation.

### 📦 Deprecating an Entire Module

Use `deprecated_module()` at the bottom of a module you are retiring. Three modes are supported.

**Mode 1 — in-place warn** (keep the module, warn on every public attribute access):

```python
# phmdoctest:skip — CI template: replace old_calculator with your actual module
# old_calculator.py
from deprecate import deprecated_module

def add(a: float, b: float) -> float:
    return a + b

# Call once at the bottom — warns on every public attribute access, including real ones.
# `__name__` is passed explicitly here; it is optional (auto-detected from the caller frame when omitted),
# but passing it is the robust idiom — auto-detection relies on `sys._getframe` and only works when the
# call sits directly in the module body, not when routed through a helper.
deprecated_module(__name__, deprecated_in="2.0", remove_in="3.0", message_template="Use `new_calculator` instead.")
# old_calculator.add(1, 2)  # warns: FutureWarning, returns 3
```

**Mode 2 — redirect** (forward missing-attr lookups to a replacement module, useful when renaming):

```python
# phmdoctest:skip — CI template: replace new_calculator with your actual module
# old_calculator.py
import new_calculator as _new_calculator
from deprecate import deprecated_module

deprecated_module(
    __name__,  # optional — auto-detected when omitted; see Mode 1 note above
    target=_new_calculator,  # all unknown attr access forwarded here
    deprecated_in="2.0",
    remove_in="3.0",
    message_template="Use `new_calculator` instead.",
)
# old_calculator.add(1, 2)  # warns: FutureWarning, returns new_calculator.add(1, 2)
```

**Mode 3 — parent alias** (expose old sub-module name on the parent package via `deprecated_instance`):

```python
# phmdoctest:skip — CI template: replace my_package with your actual package
# my_package/__init__.py
import my_package.new_calculator as _new_calculator
from deprecate import deprecated_instance

old_utils = deprecated_instance(
    _new_calculator,
    name="old_utils",
    deprecated_in="2.0",
    remove_in="3.0",
    message="Use `my_package.new_calculator` instead.",
)
# my_package.old_utils.add(1, 2)  # warns: FutureWarning
```

> [!NOTE]
>
> **Star imports also warn:** `from old_calculator import *` still emits a `FutureWarning`. CPython's `IMPORT_STAR` bytecode calls `getattr(module, name)` for each public name pulled in, so it routes through the same `__getattribute__` interception as any other attribute access — one warning per pulled-in public name. This closes a gap a PEP 562 `__getattr__` hook would otherwise leave open.

### 🌀 Async functions

`@deprecated` works natively on `async def` functions. The resulting wrapper is itself `async def`, so `inspect.iscoroutinefunction(wrapper)` returns `True` and asyncio frameworks (FastAPI, `asyncio.run`, `asyncio.gather`) recognise it. All three `TargetMode` variants work; the deprecation warning fires when the coroutine is awaited, not when the wrapper is called.

```python
import asyncio
from deprecate import TargetMode, deprecated, void

# NEW/FUTURE API
async def download(url: str) -> bytes:
    return url.encode()

# 1) target=<callable> — forward to a replacement async function
@deprecated(target=download, deprecated_in="0.9", remove_in="1.0")
async def fetch(url: str) -> bytes:
 """Deprecated — use download() instead."""
 return void(url)

# 2) TargetMode.NOTIFY — warn callers; the async body still runs
@deprecated(deprecated_in="0.9", remove_in="1.0")
async def ping() -> str:
    """Deprecated — going away; remove call sites."""
    return "pong"

# 3) TargetMode.ARGS_REMAP — rename an argument within the same async function
@deprecated(
    target=TargetMode.ARGS_REMAP,
    args_mapping={"endpoint": "url"},
    deprecated_in="0.9",
    remove_in="1.0",
)
async def fetch_data(endpoint: str = "", url: str = "") -> bytes:
    """Deprecated argument `endpoint` renamed to `url`."""
    return url.encode()

asyncio.run(fetch("https://example.com"))
asyncio.run(ping())
print(asyncio.run(fetch_data(endpoint="https://example.com")))
```

<details>
 <summary>Output: <code>asyncio.run(fetch_data(endpoint="https://example.com"))</code></summary>

```
b'https://example.com'
```

</details>

> [!NOTE]
>
> `@deprecated` also supports **async generator functions** (`async def` + `yield`). The warning fires when the wrapper is called and callers keep iterating with `async for`. For framework introspection and exact async warning-count caveats, see [Async functions](https://borda.github.io/pyDeprecate/stable/guide/async.html) and [Troubleshooting](https://borda.github.io/pyDeprecate/stable/troubleshooting.html#concurrent-async-calls-and-warning-counts).

## 🔇 Understanding the `void()` Helper

When using `@deprecated` with a `target` function, the deprecated function's body is never executed—all calls are automatically forwarded. However, your IDE might complain about "unused parameters". The `void()` helper function silences these warnings:

```python
# NEW API — adds two integers and returns the sum
def add_values(a: int, b: int) -> int:
    return a + b

# ---------------------------

from deprecate import deprecated, void

# DEPRECATED API — `add` replaced by `add_values`
@deprecated(target=add_values, deprecated_in="1.0", remove_in="2.0")
def add(a: int, b: int) -> int:
    return void(a, b)  # Tells IDE: "Yes, I know these parameters aren't used"
    # call is forwarded to add_values

# Alternative: You can also use pass or just a docstring
@deprecated(target=add_values, deprecated_in="1.0", remove_in="2.0")
def add_v1(a: int, b: int) -> int:
    """Just a docstring works too."""
    pass  # This also works

print(add_v1(2, 3))
```

<details>
 <summary>Output: <code>add_v1(2, 3)</code></summary>

```
5
```

</details>

> [!TIP]
>
> `void()` is purely for IDE convenience and has no runtime effect. It simply returns `None` after accepting any arguments.

## 🔍 Audit

Deprecations are only as good as the hygiene around them. The `deprecate.audit` module provides utilities for verifying that deprecated wrappers are correctly configured, that removal deadlines are actually enforced, and that chains of deprecated-to-deprecated calls don't silently pile up. These tools are designed to run in CI pipelines and test suites, catching problems before they reach users.

> [!NOTE]
>
> **Renamed in v0.6**: `find_deprecated_callables` → `find_deprecation_wrappers`, `validate_deprecated_callable` → `validate_deprecation_wrapper`, `DeprecatedCallableInfo` → `DeprecationWrapperInfo`. The old names are still exported for backwards compatibility but will be removed in v1.0.

### Validating Wrapper Configuration

During development, you may want to verify that your deprecated wrappers are configured correctly. pyDeprecate provides two utilities for this: `validate_deprecation_wrapper()` for inspecting a single function, and `find_deprecation_wrappers()` for scanning an entire package.

The `DeprecationWrapperInfo` dataclass contains:

- `module`: Module name where the function is defined (empty for direct validation)
- `function`: Function name
- `deprecated_info`: The `__deprecated__` attribute dict from the decorator
- `invalid_args`: List of args_mapping keys that don't exist in the function signature
- `empty_args_mapping`: True if args_mapping is None or empty (no argument remapping)
- `identity_args_mapping`: List of args where key equals value (e.g., `{'arg': 'arg'}` - no effect)
- `self_reference`: True if target points to the same function (self-reference)
- `no_effect`: True if wrapper has zero impact (self-reference, empty mapping, or all identity)
- `empty_deprecated_in`: True if `deprecated_in` is absent (CI misconfiguration signal — missing introductory version metadata)

<details>
<summary>Validating a Single Function</summary>

The `validate_deprecation_wrapper()` utility extracts the configuration from the function's `__deprecated__` attribute and returns a `DeprecationWrapperInfo` dataclass that helps you identify configurations that would make your deprecation wrapper have zero impact:

```python
from deprecate import DeprecationWrapperInfo, TargetMode, deprecated, validate_deprecation_wrapper

# Define your deprecated function
@deprecated(target=TargetMode.ARGS_REMAP, args_mapping={"old_arg": "new_arg"}, deprecated_in="1.0")
def my_func(old_arg: int = 0, new_arg: int = 0) -> int:
    return new_arg

# Validate the configuration - automatically extracts `args_mapping` and target from the decorator
result = validate_deprecation_wrapper(my_func)

# DeprecationWrapperInfo(
#   function='my_func',
#   invalid_args=[],
#   empty_args_mapping=False,
#   identity_args_mapping=[],
#   self_reference=False,
#   no_effect=False
# )

# Example: Function with invalid args_mapping
@deprecated(target=TargetMode.ARGS_REMAP, args_mapping={"nonexistent": "new_arg"}, deprecated_in="1.0")
def bad_func(real_arg: int = 0) -> int:
    return real_arg

result = validate_deprecation_wrapper(bad_func)
# result.invalid_args == ['nonexistent']
print(result)

# Example: Function with empty mapping (no effect)
@deprecated(target=TargetMode.ARGS_REMAP, args_mapping={}, deprecated_in="1.0")
def empty_func(arg: int = 0) -> int:
    return arg

result = validate_deprecation_wrapper(empty_func)
# result.empty_args_mapping == True, result.no_effect == True
print(result)

# Quick check if wrapper has any effect
if result.no_effect:
    print("Warning: This wrapper configuration has zero impact!")
```

</details>

<details>
<summary>Scanning a Package for Deprecated Wrappers</summary>

The `find_deprecation_wrappers()` utility scans an entire package or module and returns a list of `DeprecationWrapperInfo` dataclasses:

```python
from deprecate import find_deprecation_wrappers

# For testing purposes, we use the test module; normally you would import your own package
from tests import collection_deprecate as my_package

# Scan an entire package for deprecated wrappers
results = find_deprecation_wrappers(my_package)

# Or scan using a string module path
results = find_deprecation_wrappers("tests.collection_deprecate")

# Check results - each item is a DeprecationWrapperInfo dataclass
for r in results:
    print(f"{r.module}.{r.function}: no_effect={r.no_effect}")
    if r.no_effect:
        print(f"  Warning: This wrapper has zero impact!")
        print(f"  invalid_args: {r.invalid_args}, identity_args_mapping: {r.identity_args_mapping}")

# Filter to only ineffective wrappers
ineffective = [r for r in results if r.no_effect]
if ineffective:
    print(f"Found {len(ineffective)} deprecated wrappers with zero impact!")
```

</details>

<details>
<summary>Generating Reports by Issue Type</summary>

Group validation results by issue type for better reporting:

```python
from deprecate import find_deprecation_wrappers

# For testing purposes, we use the test module; normally you would import your own package
from tests import collection_deprecate as my_package

results = find_deprecation_wrappers(my_package)

# Group by issue type (using dataclass attribute access)
wrong_args = [r for r in results if r.invalid_args]
identity_mappings = [r for r in results if r.identity_args_mapping]
self_refs = [r for r in results if r.self_reference]

print(f"=== Deprecation Validation Report ===")
print(f"Wrong arguments: {len(wrong_args)}")
print(f"Identity mappings: {len(identity_mappings)}")
print(f"Self-references: {len(self_refs)}")
```

</details>

### Generating Deprecation Tables

If you want docs-friendly summaries, `generate_deprecation_table()` renders the discovered wrapper metadata as Markdown tables. The report includes deprecated class members such as methods and constructors, so wrapper metadata remains the single source of truth.

It supports two styles via `style=`:

The **Current Status** column uses these labels:

| Status                    | Meaning                                                                   |
| ------------------------- | ------------------------------------------------------------------------- |
| 🕒 Scheduled Deprecation  | Current version is before `deprecated_in` — not yet active                |
| ℹ️ No Removal Target      | No `remove_in` set — no scheduled removal                                 |
| ⚪ Status Unknown         | `packaging` not installed or `current_version` not resolvable             |
| ⚪ Invalid Removal Target | `remove_in` cannot be parsed as a PEP 440 version                         |
| 📢 Deprecation Active     | Between `deprecated_in` and `remove_in` — still in the deprecation window |
| ⏰ Removal Imminent       | Dev/alpha/beta pre-release of the `remove_in` base version                |
| 🔔 Remove Before Release  | RC pre-release of the `remove_in` base version                            |
| 💥 Past Removal Date      | Current version ≥ `remove_in` — zombie code that should be deleted        |

```python
from tests import collection_deprecate as my_package
from deprecate import generate_deprecation_table

report = generate_deprecation_table(my_package, current_version="1.5", recursive=False)
```

> **Current version: 1.5**
>
> | Original API                                | API Type     | New API                         | Deprecated | Remove | Current Status           |
> | :------------------------------------------ | :----------- | :------------------------------ | :--------: | :----: | :----------------------- |
> | `my_package.depr_func_same_version`         | callable     | `—`                             |    v2.0    |  v3.0  | 🕒 Scheduled Deprecation |
> | `my_package.ServiceCls.old_redirect_method` | class method | `my_package.ServiceCls.compute` |    v1.0    |  v2.0  | 📢 Deprecation Active    |
> | `my_package.depr_pow_args`                  | callable     | `my_package.base_pow_args`      |    v1.0    |  v1.3  | 💥 Past Removal Date     |
> | `my_package.depr_func_no_remove_in`         | callable     | `—`                             |    v1.0    |   —    | ℹ️ No Removal Target     |

<details>
<summary>Using the CLI</summary>

You can also use the CLI to validate your deprecations directly from the command line.

The CLI requires the `cli` extra (includes `fire` and `rich`). Install it with:

```bash
pip install 'pyDeprecate[audit,cli]'
```

The CLI has five subcommands.

```bash
# check — wrapper config + deprecated-to-deprecated chains (default)
pydeprecate check path/to/your/package
pydeprecate path/to/your/package          # equivalent shorthand

# expiry — wrappers past their remove_in deadline
# requires: pip install 'pyDeprecate[audit]'
pydeprecate expiry path/to/your/package --version 2.0.0
pydeprecate expiry path/to/your/package   # auto-detects version from the package

# chains — deprecated-to-deprecated forwarding chains only
pydeprecate chains path/to/your/package

# all — single scan running check + expiry + chains, then appends a deprecation table
pydeprecate all path/to/your/package --version 2.0.0

# status — print a markdown deprecation status table (standalone, no checks)
pydeprecate status path/to/your/package
pydeprecate status path/to/your/package --style matrix
pydeprecate status path/to/your/package --version 2.0.0 --output DEPRECATIONS.md
```

**Common flags** (all subcommands): `--norecursive` scans the top-level module only. `check`, `expiry`, `chains`, and `all` also accept `--exit-zero` to always exit `0` even when issues are found. `expiry`, `all`, and `status` also accept `--version VERSION` to set the current version explicitly. `status` additionally accepts `--style compact|matrix` (default `compact`) and `--output FILE` to also save the markdown to that file.

**Quick demo** using pyDeprecate's own test fixtures (no package setup needed):

```bash
# Run all checks + deprecation table on the bundled test fixtures
pydeprecate all tests --version 1.2
# Standalone deprecation table only
pydeprecate status tests --version 1.2
```

`tests/` contains pyDeprecate's own deprecation fixtures — useful as a live demo without needing your own package. Note: `expiry` and `chains` (run as part of `all`) require an importable package name rather than a plain directory path.

**Example: catching a deprecated-to-deprecated chain**

```
$ pydeprecate chains src/mypackage
⚠  Deprecated chain detected: old_fn → legacy_fn → new_fn
   old_fn is deprecated and forwards to legacy_fn, which is also deprecated.
   Update old_fn to forward directly to new_fn.
```

**Example: combined one-liner scan across all checks**

```
$ pydeprecate all src/mypackage
✓ check:  12 wrappers validated, 0 misconfigured
⚠ expiry: 2 wrappers past remove_in deadline
✓ chains: no deprecated→deprecated chains detected
```

</details>

<details>
<summary>CI/pytest Integration</summary>

Use in pytest to validate your package's deprecation wrappers:

```python
import warnings

import pytest
from deprecate import find_deprecation_wrappers

# For testing purposes, we use the test module; normally you would import your own package
from tests import collection_deprecate as my_package

def test_deprecated_wrappers_are_valid():
    """Validate all deprecated wrappers have proper configuration."""
    results = find_deprecation_wrappers(my_package)

# Collect issues — wrong arg names are errors, identity mappings are worth a warning
    wrong_args = [r for r in results if r.invalid_args]
    identity_mappings = [r for r in results if r.identity_args_mapping]

# Raise errors for wrong arguments (critical issues)
    if wrong_args:
        for r in wrong_args:
            print(f"ERROR: {r.module}.{r.function} has invalid args: {r.invalid_args}")
        pytest.fail(f"Found {len(wrong_args)} deprecated wrappers with invalid arguments")

# Warn for identity mappings (less severe)
    for r in identity_mappings:
        warnings.warn(f"{r.function} has identity mapping", UserWarning)
```

</details>

### ⏰ Enforcing Deprecation Removal Deadlines

When you deprecate code with a `remove_in` version, you're making a commitment to remove that code when that version is reached. However, it's easy to forget to actually remove the code—leading to "zombie code" that lingers past its scheduled removal.

pyDeprecate provides enforcement utilities to detect and prevent zombie code in your CI/CD pipeline:

The `validate_deprecation_expiry()` utility scans an entire module or package for expired deprecations:

<details>
<summary>Example: scanning a package for expired removal deadlines</summary>

```python
from deprecate import validate_deprecation_expiry

# For testing purposes, we use the test module; normally you would import your own package
from tests import collection_deprecate as my_package

# Scan your package for expired deprecations - using early-version that won't have expirations
expired = validate_deprecation_expiry(my_package, "0.2")
print(f"Found {len(expired)} expired")  # Returns a list of error messages (empty list = no expired)

# Example with expired deprecations found (using later-version)
expired = validate_deprecation_expiry(my_package, "0.5")
print(f"Found {len(expired)} expired")

# Auto-detect version from package metadata (mocked for demo)
from unittest.mock import patch

with patch("importlib.metadata.version", return_value="0.3"):
    expired = validate_deprecation_expiry(my_package)  # Automatically detects version
    print(f"Found {len(expired)} expired")

# Control recursion
expired = validate_deprecation_expiry(my_package, "0.1", recursive=False)  # Only scan top-level module
print(f"Found {len(expired)} expired")
```

</details>

<details>
 <summary>Output: expired count per scanned version</summary>

```
Found 14 expired
Found 31 expired
Found 17 expired
Found 0 expired
```

</details>

<details>
<summary>CI/pytest Integration for Expiry Enforcement</summary>

Integrate expiry checks into your test suite to catch zombie code automatically:

```python
import pytest
from deprecate import validate_deprecation_expiry

# For testing purposes, we use the test module; normally you would import your own package
from tests import collection_deprecate as my_package

def test_no_zombie_deprecations():
    """Ensure all deprecated code is removed when it reaches its deadline."""
    # Use your package's actual version - for this example we use a test version
    current_version = "0.5"  # Replace with: from mypackage import __version__

expired = validate_deprecation_expiry(my_package, current_version)

if expired:
        error_msg = "Found deprecated code past its removal deadline:\n"
        for msg in expired:
            error_msg += f"  - {msg}\n"
        pytest.fail(error_msg)

# Alternative: Use a fixture to run on every test session
# For testing purposes, we use the test module; normally you would import your own package
@pytest.fixture(scope="session", autouse=True)
def enforce_deprecation_deadlines():
    """Automatically check for zombie code before running any tests."""
    from tests import collection_deprecate as my_package

current_version = "0.5"  # Replace with: from mypackage import __version__
    expired = validate_deprecation_expiry(my_package, current_version)
    if expired:
        raise AssertionError(
            f"Cannot run tests: {len(expired)} deprecated callables past removal deadline. "
            f"Remove these functions first: {expired}"
        )
```

</details>

> [!TIP]
>
> - Callables without `remove_in` are skipped (warnings-only deprecations are allowed)
> - Callables with an unparsable `remove_in` version string emit a `UserWarning` naming the callable; the scan continues for the rest
> - PEP 440 versioning is used for comparison (e.g., "2.0.0" > "1.9.5")
> - Pre-release versions are handled correctly (e.g., "1.5.0a1" < "1.5.0")

### 🔗 Detecting Deprecation Chains

When refactoring code, it's easy to create "lazy" deprecated wrappers that call other deprecated functions instead of calling the new target directly. This creates deprecation chains that defeat the purpose of deprecation.

The `validate_deprecation_chains()` utility scans a module or package for deprecated functions whose `target` is itself a deprecated callable. Such chains are wasteful: the outer wrapper should point directly to the final (non-deprecated) implementation. Detection is purely metadata-based — no source-code inspection.

<details>
<summary>Example: Detecting Both Chain Types</summary>

```python
from deprecate import TargetMode, deprecated, validate_deprecation_wrapper, void

def new_power(base: float, exponent: float = 2) -> float:
    return base**exponent

# deprecated forwarder — targets new_power directly
@deprecated(target=new_power, deprecated_in="1.0", remove_in="2.0")
def power_v2(base: float, exponent: float = 2) -> float:
    void(base, exponent)

# self-deprecation — renames old arg "exp" -> "exponent" within the same function
@deprecated(TargetMode.ARGS_REMAP, deprecated_in="1.0", remove_in="2.0", args_mapping={"exp": "exponent"})
def legacy_power(base: float, exp: float = 2, exponent: float = 2) -> float:
    return base**exponent

# BAD: targets power_v2 (another deprecated forwarder) — ChainType.TARGET
# SOLUTION: point directly to new_power
@deprecated(target=power_v2, deprecated_in="1.5", remove_in="2.5")
def caller_target_chain(base: float, exponent: float = 2) -> float:  # ❌
    return void(base, exponent)

# BAD: targets legacy_power (target=TargetMode.ARGS_REMAP with arg renaming) — ChainType.STACKED
# Mappings chain: "power" -> "exp" -> "exponent" — must be composed.
# SOLUTION: target=new_power, args_mapping={"power": "exponent"}
@deprecated(target=legacy_power, deprecated_in="1.5", remove_in="2.5", args_mapping={"power": "exp"})
def caller_stacked_chain(base: float, power: float = 2) -> float:  # ❌
    return void(base, power)

# GOOD: targets final implementation directly with composed mapping
@deprecated(target=new_power, deprecated_in="1.5", remove_in="2.5", args_mapping={"power": "exponent"})
def caller_direct(base: float, power: float = 2) -> float:  # ✅
    return void(base, power)

for func in (caller_target_chain, caller_stacked_chain, caller_direct):
    info = validate_deprecation_wrapper(func)
    print(f"{func.__name__}: {info.chain_type}")
```

</details>

<details>
 <summary>Output: chain types</summary>

```
caller_target_chain: ChainType.TARGET
caller_stacked_chain: ChainType.STACKED
caller_direct: None
```

</details>

<details>
<summary>CI/pytest Integration for Chain Detection</summary>

Integrate chain detection into your test suite to prevent deprecated-to-deprecated forwarding:

```python
import pytest
from deprecate import validate_deprecation_chains

# normally you would import your own package
from tests import collection_chains as my_package

def test_no_deprecation_chains():
    """Ensure no deprecated function targets another deprecated function."""
    issues = validate_deprecation_chains(my_package)

if issues:
        lines = [
            f"  - {i.function}: target '{getattr(i.deprecated_info['target'], '__name__', repr(i.deprecated_info['target']))}' is deprecated"
            for i in issues
        ]
        pytest.fail("Found deprecation chains:\n" + "\n".join(lines))

# Alternative: session-scoped auto-use fixture
@pytest.fixture(scope="session", autouse=True)
def enforce_no_deprecation_chains():
    from tests import collection_chains as my_package

issues = validate_deprecation_chains(my_package)
    if issues:
        raise AssertionError(f"Found {len(issues)} deprecation chain(s). Fix before running tests.")
```

</details>

> [!TIP]
>
> - The function scans all deprecated functions found by `find_deprecation_wrappers()`
> - Returns `list[DeprecationWrapperInfo]` — each entry has `chain_type` set to a `ChainType` enum value
> - `ChainType.TARGET` — target is a deprecated callable that forwards to another function; fix by pointing directly to the final target
> - `ChainType.STACKED` — mappings chain through multiple hops and must be composed; includes:
>   - Callable target is itself `@deprecated(TargetMode.ARGS_REMAP, args_mapping=...)` (self-renaming) — mappings compose across hops
>   - Stacked `@deprecated(TargetMode.ARGS_REMAP, args_mapping=...)` on the same function — merge into one decorator with combined `args_mapping`
>   - `deprecated_class(attrs_mapping=...)` where one deprecated attribute redirects to another deprecated attribute alias
> - Use `recursive=False` to scan only the top-level module

### Detecting Positional-Only Incompatible Mappings

The `check` subcommand surfaces `deprecated_class` proxies whose `args_mapping` remaps a deprecated kwarg to a `POSITIONAL_ONLY` constructor parameter. The proxy forwards those remapped values positionally to the constructor, so the mapping works even for required positional-only parameters, frozen dataclasses, and classes with `__post_init__` logic — the finding is an advisory visibility signal, not a failure.

```bash
pydeprecate check my_package
# or as part of a full scan:
pydeprecate all my_package
```

> [!TIP]
>
> - The proxy forwards remapped values positionally to the constructor at call time; `pydeprecate check` surfaces the pattern at CI time as an advisory signal
> - To silence the decoration-time `UserWarning`: use `attrs_mapping` instead of `args_mapping` for `POSITIONAL_ONLY` parameters, or restructure the target constructor to accept keyword arguments
> - For programmatic use: `validate_mapping_compatibility(module)` returns `list[DeprecationWrapperInfo]` where `args_mapping_positional_only` is non-empty

## 🧪 Testing Deprecated Code

pyDeprecate provides utilities to help you test deprecated code properly:

```python
from deprecate import deprecated, assert_no_warnings, void
import pytest

# NEW API — doubles the input value
def score_predictions(x: int) -> int:
    return x * 2

# DEPRECATED API — `score` replaced by `score_predictions`
@deprecated(target=score_predictions, deprecated_in="1.0", remove_in="2.0")
def score(x: int) -> int:
    pass

# DEPRECATED API — `score_v2` replaced by `score_predictions`
@deprecated(target=score_predictions, deprecated_in="1.0", remove_in="2.0")
def score_v2(x: int) -> int:
    return void(x)

def test_deprecated_function_shows_warning():
    """Verify the deprecation warning is shown."""
    with pytest.warns(FutureWarning, match="score.*deprecated"):
        result = score(42)
    assert result == 84

def test_new_function_no_warning():
    """Verify new function doesn't trigger warnings."""
    with assert_no_warnings(FutureWarning):
        result = score_predictions(42)
    assert result == 84

def test_no_warning_after_first_call():
    """By default, warnings are shown only once per function."""
    # First call shows warning
    with pytest.warns(FutureWarning):
        score_v2(1)

# Subsequent calls don't show warning (by default num_warns=1)
    with assert_no_warnings(FutureWarning):
        score_v2(2)

# call the tests for CI demonstration/validation
test_deprecated_function_shows_warning()
test_new_function_no_warning()
test_no_warning_after_first_call()
```

<details>
<summary>Advanced: Control warning frequency</summary>

```python
# Minimal replacement implementation used in examples
def score_predictions(x: int) -> int:
    return x * 2

# ---------------------------

from deprecate import deprecated

# Show warning every time (useful for critical deprecations)
@deprecated(target=score_predictions, deprecated_in="1.0", remove_in="2.0", num_warns=-1)
def predict(x: int) -> int:
    pass

# Show warning N times total
@deprecated(target=score_predictions, deprecated_in="1.0", remove_in="2.0", num_warns=5)
def predict_batch(x: int) -> int:
    pass

print(predict_batch(1))
```

</details>

<details>
 <summary>Output: <code>predict_batch(1)</code></summary>

```
2
```

</details>

## 🔧 Troubleshooting

### ⚠ UserWarning: `` `@deprecated` on class … now dispatches to `@deprecated_class` ``

**Not a problem** — since v0.12, `@deprecated` on a class is first-class supported and permanent: it dispatches to `@deprecated_class()` and produces an identical `_DeprecatedProxy`. The `UserWarning` is a one-time informational notice, fired at most once per class (keyed by module + qualified name — same-named classes in different modules each warn) per process, telling you that the dispatch happened. Only this notice — not the dispatch support — is removed entirely, in v1.0.

**To quiet it:** apply `@deprecated_class()` directly (same result, no notice, and required to reach class-only options such as `attrs_mapping`), or pass `stream=None`.

<details>
<summary>Solution</summary>

```python
from deprecate import TargetMode, deprecated, deprecated_class
from enum import Enum

# Preferred: use @deprecated_class directly for classes — identical result, no notice
@deprecated_class(target=TargetMode.NOTIFY, deprecated_in="1.0", remove_in="2.0")
class MyClass:
    pass

@deprecated_class(target=TargetMode.NOTIFY, deprecated_in="1.0", remove_in="2.0")
class MyEnum(Enum):
    A = 1
    B = 2

# Alternative: decorate __init__ to warn at instantiation while keeping the class name
from deprecate import deprecated

class MyOtherClass:
    @deprecated(target=TargetMode.NOTIFY, deprecated_in="1.0", remove_in="2.0")
    def __init__(self, x: int) -> None:
        self.x = x  # body still executes; warning fires on every new MyOtherClass(...)

print(MyOtherClass(42).x)
```

</details>

<details>
 <summary>Output: <code>MyOtherClass(42).x</code></summary>

```
42
```

</details>

### ❗ TypeError: `Failed mapping`

**Problem:** `TypeError: Failed mapping of 'my_func', arguments not accepted by target: ['old_arg']`

**Cause:** Your deprecated function has arguments that the target function doesn't accept.

<details>
<summary>Solutions</summary>

1. **Skip the argument** (if it's no longer needed):

```python
   # define a target that ignores the extra arg
   def new_func(required_arg: int, **kwargs) -> int:
       return required_arg * 2

# ---------------------------

from deprecate import deprecated

# None means skip this argument
   @deprecated(target=new_func, args_mapping={"old_arg": None}, deprecated_in="1.0", remove_in="2.0")
   def old_func(old_arg: int, new_arg: int) -> int:
       pass
   ```

2. **Rename the argument** (if target uses different name):

```python
   def new_func(new_name: int) -> int:
       return new_name * 2

# ---------------------------

from deprecate import deprecated

# Map old to new
   @deprecated(target=new_func, args_mapping={"old_name": "new_name"}, deprecated_in="1.0", remove_in="2.0")
   def old_func(old_name: int) -> int:
       pass
   ```

3. **Use `TargetMode.ARGS_REMAP` for self-deprecation** (deprecate argument of same function):

```python
   from deprecate import TargetMode, deprecated

# Deprecate within same function
   @deprecated(target=TargetMode.ARGS_REMAP, args_mapping={"old_arg": "new_arg"}, deprecated_in="1.0", remove_in="2.0")
   def my_func(old_arg: int = 0, new_arg: int = 0) -> int:
       return new_arg * 2
   ```

</details>

### ❗ TypeError: `User function 'should_ship' shall return bool`

**Problem:** `TypeError: User function 'should_ship' shall return bool, but got: <type>`

**Cause:** When using `skip_if` with a callable, the function must return a boolean value.

<details>
<summary>Solution</summary>

```python
# Minimal replacement function for examples
def get_status() -> str:
    return "Hi!"

# ---------------------------

from deprecate import deprecated_callable

# Correct: function returns bool
def should_skip() -> bool:
    return False  # replace with your condition

@deprecated_callable(target=get_status, skip_if=should_skip, deprecated_in="1.0", remove_in="2.0")
def infer():
    pass

# Also correct: use a lambda
@deprecated_callable(target=get_status, skip_if=lambda: False, deprecated_in="1.0", remove_in="2.0")
def infer_v2():
    pass

print(infer_v2())
```

</details>

<details>
 <summary>Output: <code>infer_v2()</code></summary>

```
Hi!
```

</details>

### ⚠️ Warning Not Showing

**Problem:** You don't see the deprecation warning.

**Cause:** By default, warnings are shown **only once per function** (`num_warns=1`) to prevent log spam. For per-argument deprecation (when using `args_mapping` with `TargetMode.ARGS_REMAP`), each deprecated argument has its own warning counter, meaning warnings for different arguments are tracked independently.

<details>
<summary>Solutions</summary>

```python
# Minimal replacement function for examples
def score_predictions(x: int) -> int:
    return x * 2

# ---------------------------

from deprecate import deprecated

# Show warning every time
@deprecated(target=score_predictions, deprecated_in="1.0", remove_in="2.0", num_warns=-1)  # -1 means unlimited
def predict():
    pass

# Show warning N times total
@deprecated(target=score_predictions, deprecated_in="1.0", remove_in="2.0", num_warns=5)  # Show 5 times
def predict_batch():
    pass

print(callable(predict_batch))
```

<details>
 <summary>Output: <code>callable(predict_batch)</code></summary>

```
True
```

</details>

### 📦 Deprecation Not Working Across Modules

**Problem:** The deprecation notice shows an unexpected path when a function is moved to a different module.

**Cause:** pyDeprecate resolves the target path from `target.__module__` and `target.__qualname__` at decoration time — not at call time. If the target is imported via an alias or re-export at the point where `@deprecated` is applied, the stored path reflects the alias, not the canonical location.

**Solution:** Import the target from its canonical module location before applying `@deprecated`. The deprecation notice will then show the fully-qualified path where the function actually lives.

## 🤝 Contributing

Have you faced this issue in the past or are you facing it now? Do you have good ideas for improvement? All contributions are welcome!

Please read our [Contributing Guide](.github/CONTRIBUTING.md) for details on how to contribute, and our [Code of Conduct](.github/CODE_OF_CONDUCT.md) for community guidelines.

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