experimental

Yet another way of messing with non-existent features in Python.

This is a personal __future__-like collection of features that will only be active if imported from __experimental__ near the top of a Python file. Some of those features include:

• Late-bound function argument defaults
  • Based on PEP 671.
  • Currently, the late-bound expressions must be surrounded in parentheses, unlike the syntax proposed in the relevant PEP.
• Module-level and context manager-level lazy imports
  • Based on PEP 690 and several other attempts at lazy importing.
  • Currently, from imports are evaluated eagerly.
• Inline import expressions
  • Based on import-expression.
• Elision of typing.cast/typing_extensions.cast
  • Based on past discussions had about possibly eliminating the cost of cast.

They shouldn't be mutually exclusive syntax-wise.

Installation

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

I don't see a reason to put this on PyPI as of now.

Examples

"""example1.py"""
from __experimental__ import late_bound_arg_defaults

def bisect_right(a, x, lo=0, hi=>(len(a)), *, key=None):
    # If nothing is passed in for hi, only then will it evaluate as len(a).
    # Late-bound defaults will be evaluated in left-to-right order.
    ...


"""example2.py"""
from __experimental__ import inline_import

# This will import the collections module and use it without having to place
# an import statement at the top of the file.
assert collections!.Counter("bccdddeeee") == {'e': 4, 'd': 3, 'c': 2, 'b': 1}


"""example3.py"""
from __experimental__ import lazy_import

# All module imports within this file henceforth should be performed lazily,
# i.e. delaying module load until accessing an attribute from the module.
...

Caveats

Registration

This package uses a .pth file to register an import hook on interpreter startup. The hook replaces the built-in file finder's path hook on sys.path_hooks. That should work fine if you're using a regular setup with site packages, where that .pth file should end up.

However, if your environment is atypical, you might need to manually register that finder to have your code be processed by this package. Do so in a file away from the rest of your code, before any of it executes. For example:

import __experimental__
__experimental__.install()
import your_actual_module

Documentation

See the docstrings and comments in the code. They're currently a little bare, but they will improve over time.

Why?

It's fun. It's also a learning experience in manipulating Python via import hooks, AST transformations, token stream transformations, and more.

Acknowledgements

• aroberge's ideas package, which introduced me to the idea of modifying Python like this.
• asottile's future packages, including things like future-fstrings, that are practical applications showcasing the usefulness of these kinds of transformations ("memes" though they may be).
• RocketRace's hoopy and custom-literals packages, which are much more interesting, complex, and featured Python manipulations.
• Those who wrote the original PEPs and packages that this attempts to (re)implement (see the links in the overview).
• Addendum: aroberge had the idea (and the code) for an __experimental__ package well before I did, but I didn't know until well after making this.