`Counter.__init__` can't be typed safely
Nobody has claimed this yet.
Assessment
- Difficulty
- 5/5
- Estimated time
- Over a week
- Newbie friendliness
- 25/100
Research direction
Start by reviewing the Counter overload example and the proposed typing.Error behavior in this issue. No repository files or tests are identified; completion would require an agreed type-system design and a documented way to represent or diagnose the unsafe overload.
Written by the indexing model from the issue text.
Description
Counter overloads are unsafe
from collections import Counter
# no type errors reported and nothing tricky going on
a = {"a": "hello"}
b = Counter(a)
c = b.get("a", 0)
print(c + 2) # crash
and I think there isn't a way to express them safely in the current type system.
Iterable[_T] needs to be something like Iterable[_T] - Mapping[_T, ~int]
If type checkers want to address this now, it would probably have to be a special case.
Without having to worry about type intersections/differences/negations, maybe we could have a way to indicate:
"If this overload matches (after all previous overloads fail), a type error should be reported."
something like:
@overload
def __init__(self, mapping: Mapping[_T, Any], /) -> typing.Error: ...
- Dominant language
- Python
- Stars
- 1.8k
- Forks
- 302
- Avg merge
- 23h
- Merged PRs (30d)
- 8
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