tinykernel

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A minimal Python kernel so you can run Python in your Python

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# tinykernel
> A minimal Python kernel, so you can run Python in your Python.

All the clever stuff in this library is provided by Python's builtin `ast` module and compilation/exec/eval system, along with [IPython](https://ipython.org/)'s `CachingCompiler` which does some [deep magic](https://cprohm.de/article/better-test-output-with-ast-rewriting-and-a-patched-standard-library.html/). `tinykernel` just brings them together with a little glue.

## Install

With pip:

pip install tinykernel

With conda:

conda install -c fastai tinykernel

## How to use

This library provides a single class, `TinyKernel`, which is a tiny persistent kernel for Python code:

```python
k = TinyKernel()
```

Call it, passing Python code, to have the code executed in a separate Python environment:

```python
k("a=1")
```

Expressions return the value of the expression:

```python
k('a')
```

All variables are persisted across calls:

```python
k("a+=1")
k('a')
```

Multi-line inputs are supported. If the last line is an expression, it is returned:

```python
k("""import types
b = types.SimpleNamespace(foo=a)
b""")
```

namespace(foo=2)

The original source code is stored, so `inspect.getsource` works and, tracebacks have full details.

```python
k("""def f(): pass # a comment
import inspect
inspect.getsource(f)""")
```

'def f(): pass # a comment\n'

When creating a `TinyKernel`, you can pass a dict of globals to initialize the environment:

```python
k = TinyKernel(glb={'foo':'bar'})
k('foo*2')
```

'barbar'

Pass `name` to customize the string that appears in tracebacks ("kernel" by default):

```python
k = TinyKernel(name='myapp')
code = '''def f():
    return 1/0
print(f())'''
try: k(code)
except Exception as e: print(traceback.format_exc())
```

Traceback (most recent call last):
      File "<ipython-input-37-8b370e64c5cb>", line 5, in <module>
        try: k(code)
      File "/home/jhoward/git/tinykernel/tinykernel/__init__.py", line 20, in __call__
        if expr: return self._run(Expression(expr.value), nm, 'eval')
      File "/home/jhoward/git/tinykernel/tinykernel/__init__.py", line 12, in _run
        def _run(self, p, nm, mode='exec'): return eval(compiler(p, nm, mode), self.glb)
      File "<myapp--1-57331cf14e08>", line 3, in <module>
        print(f())
      File "<myapp--1-57331cf14e08>", line 2, in f
        return 1/0
    ZeroDivisionError: division by zero

## Acknowledgements

Thanks to Christopher Prohm, Matthias Bussonnier, and Aaron Meurer for their helpful insights in [this twitter thread](https://twitter.com/jeremyphoward/status/1424990665746763781).

tinykernel

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