Hello!
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)
returnSpecialized
def__init__(self, value= None):
self.value = value
def__str__(self):
ifhasattr(self, "specials"):
return(f"[{type(self)}- "+ ",".join(str(special) forspecial
inself.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
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