Repository navigation
Possible regression in 1.7 with dict unions (PEP 584) #16572
Description
There's a change for sure, but I'm having trouble figuring out if the old or new behavior is correct.
I skimmed the Mypy changelog but didn't find much about this.
Quick reproducer:
from collections.abc import Mapping
a: Mapping[str, str] = {}
{"a": "a"} | aOn 1.6: no error.
On 1.7:
a05.py:5: error: No overload variant of "__or__" of "dict" matches argument type "Mapping[str, str]" [operator]
a05.py:5: note: Possible overload variants:
a05.py:5: note: def __or__(self, dict[str, str], /) -> dict[str, str]
a05.py:5: note: def [_T1, _T2] __or__(self, dict[_T1, _T2], /) -> dict[str | _T1, str | _T2]
The PEP gives the following pseudocode for __or__:
def __or__(self, other):
if not isinstance(other, dict):
return NotImplemented
new = dict(self)
new.update(other)
return newSo I guess the new behavior might be more correct? It feels less useful though.
Activity
AlexWaygood commentedon Nov 26, 2023
Duplicate of #16489.
The behaviour change is as a result of this typeshed change: python/typeshed#10679. The new behaviour is more accurate, and the change was made to fix a false negative that was reported by a user to typeshed: python/typeshed#10678.
Tinche commentedon Nov 26, 2023
Cool, thanks. Wish we had a frozendict!
I tried searching for duplicates but I couldn't find any. GitHub issue search could be better :/