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Re-apply type annotations from .pyi stubs to your codebase.

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# retype

**!!! Note this project is no longer supported/maintained as of 2022 August 14th !!!**

Re-apply type annotations from .pyi stubs to your codebase.

## Usage

```
Usage: retype [OPTIONS] [SRC]...

Re-apply type annotations from .pyi stubs to your codebase.

Options:
  -p, --pyi-dir DIRECTORY     Where to find .pyi stubs.  [default: types]
  -t, --target-dir DIRECTORY  Where to write annotated sources.  [default:
                              typed-src]
  -i, --incremental           Allow for missing type annotations in both stubs
                              and the source.
  -q, --quiet                 Don't emit warnings, just errors.
  -a, --replace-any           Allow replacing Any annotations.
  --hg                        Post-process files to preserve implicit byte
                              literals.
  --traceback                 Show a Python traceback on error.
  --version                   Show the version and exit.
  --help                      Show this message and exit.
```

When you run `retype`, it goes through all files you passed as SRC, finds the
corresponding .pyi files in the `types/` directory, and re-applies typing annotations
from .pyi to the sources, using the Python 3 function and variable annotation syntax.
The resulting combined sources are saved in `typed-src/`.

You can also pass directories as sources, in which case `retype` will look for .py files
in them recursively.

It's smart enough to do the following:

- reapply typing imports
- reapply function argument annotations
- reapply function return value annotations
- reapply method argument and return value annotations
- reapply function-level variable annotations
- reapply module-level name annotations
- reapply module-level type aliases
- reapply class-level field annotations
- reapply instance-level field annotations
- validate existing source annotations against the .pyi file
- validate source function signatures against the .pyi file
- read function signature type comments in .pyi files
- read variable type comments in .pyi files
- consider existing source type comments as annotations
- remove duplicate type comments from source when annotations are applied
- normalize remaining type comments in the source to annotations; this is done even if
  the corresponding .pyi file is missing

## List of things to be done

- [ ] add a --backward option to output type comments instead of annotations
- [ ] handle if sys.version_info and sys.platform checks in stubs

## Design principles

- it's okay for a given .pyi file to be incomplete (gradual typing, baby!)
- it's okay for functions and classes to be out of order in .pyi files and the source
- it's an **error** for a function or class to be missing in the source
- it's an **error** for a function's signature to be incompatible between the .pyi file
  and the source
- it's an **error** for an annotation in the source to be incompatible with the .pyi
  file

## Known limitations

- Line numbers in the annotated source will no longer match original source code; this
  is because re-application of types requires copying typing imports and alias
  definitions from the .pyi file.
- While formatting of the original source will be preserved, formatting of the applied
  annotations might differ from the formatting in .pyi files.
- The source where type annotations get re-applied cannot use the legacy `print`
  statement; that wouldn't work at runtime.
- Class attribute annotations in `__init__()` methods are moved verbatim to the
  respective `__init__()` method in the implementation. They are never translated into
  class-level attribute annotations, so if that method is missing, the translation will
  fail. Similarly, class-level attribute annotations are never applied to `__init__()`
  methods.
- Forward references in .pyi files will only be properly resolved for type aliases and
  type vars (by inserting them right before they're used in the source). Other forms of
  forward references will not work in the source code due to out-of-order class and
  function definitions. Modify your .pyi files to use strings. `retype` will not
  automatically discover failing forward references and stringify them.
- Local variable annotations present in the .pyi file are transferred to the body level
  of the given function in the source. In other words, if the source defines a variable
  within a loop or a conditional statement branch, `retype` will create an value-less
  variable annotation at the beginning of the function. Use a broad type and constrain
  types in relevant code paths using `assert isinstance()` checks.
- Because of the above, existing source variable annotations and type comments buried in
  conditionals and loops will not be deduplicated (and `mypy` will complain that a name
  was already defined).
- An async function in the stub will match a regular function of the same name in the
  same scope and vice versa. This is to enable annotating async functions spelled with
  `@asyncio.coroutine`.

## Tests

Just run:

```
tox
```

## OMG, this is Python 3 only!

Relax, you can run _retype_ **as a tool** perfectly fine under Python 3.6+ even if you
want to analyze Python 2 code. This way you'll be able to parse all of the new syntax
supported on Python 3 but also _effectively all_ the Python 2 syntax at the same time.

By making the code exclusively Python 3.6+, I'm able to focus on the quality of the
checks and re-use all the nice features of the new releases (check out
[pathlib](docs.python.org/3/library/pathlib.html) or f-strings) instead of wasting
cycles on Unicode compatibility, etc.

Note: to retype modules using f-strings you need to run on Python 3.6.2+ due to
[bpo-23894](http://bugs.python.org/issue23894).

## License

MIT

## Change Log

### 20.10.0

- Mark python3.8 and python3.9 compatible

### 19.9.0

- add a module entry-point, now you can call it via `python -m retype`
- automatically all files excluded by `.gitignore` on merge of folders
- support for `ast3.num`
- fix a bug that meant the merge was not recursive in paths
- use `setup.cfg` based packaging configuration
- add PEP-517/8 declaration via `pyproject.toml`
- include license in both wheel and sdist
- this projects code base is now formatted with _black_, import ordered via _isort_, and
  uses Azure Pipelines instead of Travis (also testing on Windows and macOs)

### 17.12.0

- support --replace-any to allow replacing pre-existing `Any` annotations without
  raising errors

- bugfix: don't re-apply `# type: ignore` as an annotation if followed by another
  comment. Original patch by Shannon Zhu.

### 17.6.3

- bugfix: don't try to re-apply `# type: ignore` as a function annotation

- bugfix: support arbitrary source file encodings, patch by Michael Overmeyer.

- bugfix: support missing newlines at the end of the file, patch by Michael Overmeyer.

- bugfix: in --incremental, format default values according to PEP 8 (no spaces around
  the = sign if the type is missing)

### 17.6.2

- bugfix: --incremental didn't work with multiple arguments before

### 17.6.1

- support --incremental stub application (i.e. allow for both stubs and the source to be
  missing annotations for some arguments and/or return value)

### 17.6.0

- support async functions

- support --traceback for getting more information about internal errors

### 17.4.0

- first published version

- date-versioned

## Authors

Glued together by [Łukasz Langa](mailto:lukasz@langa.pl). Multiple improvements by
[Michael Overmeyer](mailto:m.overmeyer@yahoo.ca) and
[Bernat Gabor](mailto:gaborjbernat@gmail.com).

retype

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