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pythonpycharmpython-typing

Strange behaviour when type-hinting dict.items() in PyCharm

Say I have a function, do_something:

from typing import Sequence, Tuple, Dict

def do_something(argument: Sequence[Tuple[int, str]]):
    pass

Say I also have a dictionary, D, the keys of which are solely ints, and the values of which are solely strs:

D: Dict[int, str] = {1: 'a', 2: 'b', 3: 'c'}

In PyCharm, this will pass the type-checker with flying colours:

do_something(
    ((1, 'a'), (2, 'b'), (3, 'c'))
)

But this, according to PyCharm, fails the type-checker, despite being identical in what it produces:

do_something(tuple(D.items()))

Is this expected behaviour -- am I missing something here? -- or is this a bug with PyCharm's type-checker?

Solution

  • This is a bug in PyCharm. There are many similar bugs, e.g. this, this, this.

    In general, PyCharm is pretty clever about this. It correctly infers the type of D in your case. It also correctly infers D.items(), and then in code like for k, v in D.items(), k and v will be correctly inferred. But for some strange reason, tuple/list/sorted or sth around D.items() is buggy.

    I would always report an issue on Youtrack when you would expect that it should work.