Collections.abc types do not work like typing types

[Dr-ZeeD]

• cattrs version: 1.3.0
• Python version: Python 3.9.1
• Operating System: macOS 11.2.1

Description

Python 3.9 deprecated typing.<containers> in favor of using collections.abc.<containers>. Using collections.abc. containers does not work as expected, though.

What I Did

from collections import abc
import typing

from attr import define

from cattr import GenConverter


@define
class A:
    a: int


@define
class B:
    b: typing.MutableSequence[A]


@define
class C:
    c: abc.MutableSequence[A]


converter = GenConverter()


if __name__ == "__main__":
    a = A(1)

    b = B([a])
    print(converter.unstructure(b))

    c = C([a])
    print(converter.unstructure(c))

The actual output is:

{'b': [{'a': 1}]}
{'c': [A(a=1)]}

What I expected:

{'b': [{'a': 1}]}
{'c': [{'a': 1}]}

[Dr-ZeeD]

Also note that introducing a unstructure hook via

converter.register_unstructure_hook(
    abc.MutableSequence,
    partial(converter.unstructure, unstructure_as=typing.MutableSequence),
)

does not lead to the desired result.

However, somewhat similarly to the other issue I had raise, this might be a viable short term fix:

def _is_sequence(cls):
    return issubclass(get_origin(cls), abc.Sequence)


converter.register_unstructure_hook_func(_is_sequence, converter._unstructure_seq)
converter.register_structure_hook_func(_is_sequence, converter._structure_list)

[Tinche]

If the typing alternatives are deprecated with is worth fixing quickly. Will look into it over the next couple of days.

[Tinche]

Should be fixed in Tinche@da63135

[Dr-ZeeD]

Works like a charm. Thank you! Let me apologize in advance, I am currently formulating a new issue 😅