[Python] In Python, how to use a decorator to mark a keyword-only mandatory argument as...

So, I have a bunch of functions that all have a certain keyword argument, let's call it kw, which is mandatory and has a specific type T. However, I want to be able to call the functions without necessarily providing that keyword argument, and if it's not present I want it to be generated, probably through a decorator. Furthermore, I want my IDE to show its signature as if kw were optional.

In other words, I have functions that have a signature kind of like this:

def f(*args, kw: T, **kwargs): ...


I want their signature to look something like this to my IDE and type checker:



(Since each function might have other positional and/or keyword arguments.)

It seems to me like I should be able to have some decorator sort of like this:

def decorator(func):
sig = inspect.signature(func)
hints = get_type_hints(func)
orig_ann = hints.get("kw")
new_ann = Optional[orig_ann]

new_params = []
for param in sig.parameters.values():
if param.name == "kw":
new_params.append(
param.replace(
annotation=new_ann,
default=None,
)
)
else:
new_params.append(param)

new_sig = sig.replace(parameters=new_params)

@wraps(func)
def wrapper(*args, **kwargs):
if kwargs.get("kw") is None:
kwargs["kw"] = some_function_or_something()
return func(*args, **kwargs)

"do something to update the signature"
return wrapper


But I cannot for the life of me figure out what I would need to do to get that to happen. Is it possible? How would I do it if so?

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