https://github.com/sachaa-thanasius/experimental-late-bound-defaults

A way to mess with PEP 671 syntax in python.
https://github.com/sachaa-thanasius/experimental-late-bound-defaults

Last synced: 9 days ago
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A way to mess with PEP 671 syntax in python.

• Host: GitHub
• URL: https://github.com/sachaa-thanasius/experimental-late-bound-defaults
• Owner: Sachaa-Thanasius
• License: mit
• Created: 2024-03-30T00:33:15.000Z (9 months ago)
• Default Branch: main
• Last Pushed: 2024-03-30T14:53:47.000Z (9 months ago)
• Last Synced: 2024-03-31T03:29:49.502Z (9 months ago)
• Language: Python
• Homepage:
• Size: 21.5 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# experimental-late-bound-defaults

A way to mess with [PEP 671](https://peps.python.org/pep-0671/) syntax in python without needing a CPython fork.

## Installation

```shell

python -m pip install https://github.com/Sachaa-Thanasius/experimental-late-bound-defaults

```

# Usage

All you need is the encoding declaration at the top of your file and you're good to go for using the late binding syntax.

```python

# coding: experimental-late-bound-defaults

def example_func(

    a: int,

    b: list[int] => ([a] * a)

    c: int => (len(b) + a),

) -> tuple[list[object], int]:

    # If late-bound arguments like b and c aren't passed in, they're computed based

    # on the expressions after the '=>', in order, before the function body executes.

    assert b == ([a] * a)

    assert c == (len(b) + a)

    return c

assert example_func(5) == 10

```

## Motivation

I was annoyed with Python defaults, and resulting searches and discussion let to me being made aware of the above proposal (and [PEP 661](https://peps.python.org/pep-0671/), but I'm ignoring that for now).

I didn't want to fork CPython and change all the grammar to try this out, so I cheated with a custom codecs and tokens/AST transformation.

## Caveats

The late-bound expression must be surrounded by parentheses, unlike the syntax proposed in the PEP. This may be fixed in the future.

## Acknowledgements

Thank you to [@asottile](https://github.com/asottile) and his future packages (e.g. [future-fstrings](https://github.com/asottile-archive/future-fstrings)) for providing an outline for how to modify code like this.