POC exploring possible syntaxes for the python-ideas thread: Package kwkey and PEP 472 -- Support for indexing with keyword arguments

example.py

# coding=kw_getitem

class Helper:
    def _getitem_wrapper(self, *a, **kw):
        a_x = {0: (), 1: a}.get(len(a), (a, ))
        return self.__getitem__(*a_x, **kw)


class ObjWithGetitem(Helper):

    def __getitem__(self, key=None, foo=None, bar=None):
        print(f'{key=}  {foo=}')


def main():
    obj = ObjWithGetitem()
   
    obj[1]
    # key=1  foo=None

    obj[foo=1]
    # key=None  foo=1
    
    obj[1, foo=2]
    # key=1  foo=2
    
    obj[1, 2]
    # key=(1, 2)  foo=None
    
    obj[1, 2, foo=3]
    # key=(1, 2)  foo=3

    obj[(1, 2), foo=3]
    # key=(1, 2)  foo=3

    obj[(1, 2), 3, foo=4]
    # key=((1, 2), 3)  foo=4

    obj[**{'foo': 9}]
    # key=None  foo=9

    obj[1, 2, foo=3, xxx=5]
    # TypeError: __getitem__() got an unexpected keyword argument 'xxx'

run.py

from codecs import register, CodecInfo
import re

def wrap_subs(match):
    return f'._getitem_wrapper({match.group(1)})'

def decode(x):
    source = bytes(x).decode('utf8')
    decoded = re.sub(r'\[(.*?)\]', wrap_subs, source)
    return decoded, len(source)

register(lambda n: CodecInfo(None, decode) if n == 'kw_getitem' else None)

import example
example.main()