"function" is not assignable to "FunctionType" - is this a bug?

[Andrej730]

See example below.

import types

def test(x: types.FunctionType): pass

print(type(test) == types.FunctionType) # True

# Argument of type "(x: FunctionType) -> None"
# cannot be assigned to parameter "x" of type "FunctionType" in function "test"
#   "function" is not assignable to "FunctionType"
test(test)

The use case - was trying to add typing to old Python 2 code that doesn't have typing module and types.FunctionType is a way to document the argument is a function.

def test_x(x):
    # type: (types.FunctionType) -> None
    pass

test_x(test_x)

[erictraut]

No, this isn't a bug. The types defined in the types module should generally not be used for type checking purposes. They represent internal implementation types for Python. You should use types defined in the typing module for type annotations instead. In this case, use typing.Callable.

[Andrej730]

In my case, in Python 2 there is no typing.Callable...

[erictraut]

Pyright doesn't work with Python 2. I don't think any of the current type checkers do. Python 2 has been out of support for five years now.

[Andrej730]

It's not Python 2 only code, it just old code that supports both Python 2 & 3 and typing with comments like type: (types.FunctionType) -> None works for that case.