I'm not sure I'm addressing the right audience here, so please direct me to the appropriate channel if that's the case...

My name is Andras Tantos and I'm working on a Python library desscribing HW designs. I came across this problem of __getitem__ and co. not supporting kwargs. Apparently this extension was proposed and rejected as PEP 472.

Apart from my use-case, which is arguably a corner-case and not worth modifying the language for, I believe there are two important use-cases that are worth considering with the latest improvements in the language:

1. With the recent type-hint support, the feature could be made way more descriptive if this PEP got implemented.

For example, instead of doing the following:

    def func(in: Dict[str, int])

one could write:

    def func(in: Dict[key=str, value=int])

2. It would also make 'generic classes' much cleaner to implement, similar to the way type-hints look. Consider the following code:

class _Generic(object):

Specializations = []

@classmethod

def __getitem__(cls, *args):

name = f"Generic_{len(cls.Specializations)}"

Specialized = type(name, (cls,), {"specials": tuple(args)})

cls.Specializations.append(Specialized)

return Specialized

def __init__(self, value = None):

self.value = value

def __str__(self):

if hasattr(self, "specials"):

return(f"[{type(self)} - " + ",".join(str(special) for special in self.specials) + f"] - {self.value}")

else:

return(f"[{type(self)} - GENERIC" + f"] - {self.value}")

Generic = _Generic()

#g = Generic() - fails because of no specialization is given

s1 = Generic[12]()

s2 = Generic[42]("Hi!")

print(s1)

print(s2)

Running this simple example results in:

python3 -i python_test.py
[<class '__main__.Generic_0'> - 12] - None
[<class '__main__.Generic_1'> - 42] - Hi!

You can see how the specialized parameters got passed as well as the ones to '__init__'. Obviously, in real code the idea would be to filter generic parameters and set up 'Specialized' with the right set of methods and arguments.

Now, without kwargs support for __getitem__, it's impossible to pass named arguments to the specialization list, which greatly limits the usability of this notation.

I don't know how convincing these arguments and use-cases are for you, but could you advise me about how to start the 'ball rolling' to drum-up support for re-activating this PEP?

Thanks again,
Andras Tantos