[Python] Python: type-hinting CTypes "pointer to X" types in a way that MyPy accepts

I have a large Python binding over a C library, with complex memory management. To help with that, I have drawn up the following aliases for strings (here, you a minimal reproducible example of my definitions and the subsequent problem).

from typing import Type, TypeAlias
from ctypes import POINTER, pointer, c_char, c_char_p

#normal python string
p_useable_p_str = str

#the result of a my_str.decode("utf-8")
c_useable_p_str = bytes

#used for string literals returned by the C, which should not be freed
p_useable_c_str = c_char_p

#used for allocated strings returned by the C, which need to be freed later
c_useable_c_str = POINTER(c_char) #the problematic line

def example(hello: c_useable_c_str): # source of the MyPy error
pass


My code runs fine (memory freed properly, consistent inheritance of the above if necessary, etc) when following the above definitions+usage conventions). POINTER(c_char) has the intended behavior in the rest of the code.

However, analyzing the above with MyPy, I get:

playground.py:10: error: Variable "playground.c_useable_c_str" is not valid as a type
playground.py:10: note: See https://mypy.readthedocs.io/en/latest/common_issues.html#variables-vs-type-aliases
Found 1 error in 1 file (checked 1 source file)


I get this error for anything that uses the c_useable_c_str alias. I, of course, read the section in the documentation linked above, and tried using Type and TypeAlias in a bunch of different ways - to no avail.

The only syntax that seems to make MyPy happy is

c_useable_c_str = pointer[c_char]


However, when actually running the code with this definition of the type alias, I get the following error (not seen by MyPy, so I suspect a bug on MyPy's end, or a lack of typing in the standard):

Traceback (most recent call last):
File "/home/fulguritude/ProfessionalWork/LEDR/Orchestra-AvesTerra/Python_binding/playground2.py", line 92, in <module>
c_useable_c_str = pointer[c_char]
TypeError: 'builtin_function_or_method' object is not subscriptable


Any ideas as to how I'm supposed to make things consistent ?

TLDR: what's the valid way to type hint, and alias, a "pointer to X" with MyPy and CTypes ?

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