Type refinements are not applied to index expressions

Ran into this issue today, I believe mypy is incorrectly flagging this as an error:

from typing import Any, Dict, Optional


def rename_keys(
    original_dict: Dict[str, Any], key_mapping: Dict[str, Optional[str]]
) -> Dict[str, Any]:
    """Renames keys in the dictionary using the key_mapping. If the value in key_mapping is None then it will remove the key entirely"""
    return {
        key_mapping.get(k, k): v
        for k, v in original_dict.items()
        if k not in key_mapping or key_mapping[k] is not None
    }

output from mypy:

/tmp/mypytest.py:8: error: Key expression in dictionary comprehension has incompatible type "Optional[str]"; expected type "str"

if key_mapping.get(k) is None then it would fail the if-statement at the end of the dictionary comprehension and therefore get filtered out

if k is not in key_mapping then k is the result of the expression key_mapping.get(k,k). k can't be None because k comes from the keys of original_dict which has the type Dict[str, Any]

Versions: mypy 0.701, Python 3.7.4

no flags

Reproduisez le rapport avec la compréhension de dictionnaire rename_keys montrée en utilisant mypy 0.701 et Python 3.7.4. Suivez la manière dont les affinements de types sont traités pour la condition if et l’accès indexé, puis vérifiez que le diagnostic incompatible Optional[str] est résolu sans laisser passer le cas None.