Specifying a default of `None` for `Dict.get()` results in a type of `Any` instead of `Optional[Any]`

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#4,359 5 comments 1 reaction 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers

Research direction

Start by reproducing the two examples in the issue and inspect mypy's handling of Dict.get() type inference. Trace the relevant type-checking path and add a regression test showing that an explicit None default does not become Any; done means the revealed and return types match the intended Optional behavior.

Written by the indexing model from the issue text.

Description

bug priority-1-normal topic-type-variables

Example:

from typing import Dict

def foo(x: Dict) -> str:
    result = x.get('foo', None)
    reveal_type(result)  # E: Revealed type is 'Any'
    return result

from typing import Dict

def foo(x:Dict) -> str:
    result = x.get('foo')
    reveal_type(result)  # E: Revealed type is 'Union[Any, builtins.None]'
    return result  # E: Incompatible return value type (got "Optional[Any]", expected "str")
Dominant language
Python
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Avg merge
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Merged PRs (30d)
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