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Type checking unexpectedly passing when misusing `default` and `converter`

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还没有人认领这个 Issue。

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难度
4/5
预计耗时
3-5 天
新手友好度
25/100
Issue 类型
缺陷
描述清晰度
需要澄清
活跃度
停滞
技术栈
python
领域
tooling

调研方向

Start by running the Python 2/3 reproducer and checking the reported MyPy diagnostics for A, especially the y attribute using default=None and _convert_int. Trace whether the missing error belongs to attrs' generated typing information or to MyPy/Typeshed, and consider the issue done when the ownership and a regression check for this case are established.

由索引模型根据 Issue 内容生成。

描述

Bug Typing

I was playing around with type annotations and Attrs, and I think I may have found an issue.

Given the following Python 2/3 script:

from __future__ import absolute_import

from pprint import pprint as pp

import attr


def _convert_int(val):
    # type: (int) -> int
    if val <= 0:
        return -1
    return val


@attr.s
class A(object):
    x = attr.ib(default=0, converter=_convert_int, type=int)
    y = attr.ib(default=None, converter=_convert_int, type=int)  # `default` is incompatible with our declared `type`


def main():
    # type: () -> None
    a1 = A(5, 5)        # correct: type checks
    pp(a1)
    a2 = A(5, None)     # correct: doesn't type check
    pp(a2)
    a3 = A(5)           # incorrect: type checks but shouldn't!
    pp(a3)


if __name__ == '__main__':
    main()

I'd expect MyPy to complain about the relationship between default and converter for y. Nevertheless, I'm getting:

image

Which is one error less than expected.

Should I perhaps report this to MyPy or Typeshed as well/instead?

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