Union types for dict keys are not inferred in union context
Open
Nobody has claimed this yet.
bug
false-positive
needs discussion
priority-1-normal
topic-join-v-union
topic-union-types
- Dominant language
- Python
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Description
mypy: 0.650
Python: 3.7.1
I'm not sure if this is a bug or a new feature, however the following code is unexpected (in my mind, especially coming from TypeScript):
d = {"1": 2, 3: 4}
reveal_type(d) # builtins.dict[builtins.object*, builtins.int*]
I would have expected mypy to infer the type of d as builtins.dict[Union[builtins.str*, builtins.int*], builtins.int*].
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Research direction
Start by reproducing the reported dictionary inference with mypy 0.650 and Python 3.7.1, then trace the type inference entry point for dictionary literals. Done means the example reports a dictionary whose key type is a union of str and int, with a regression test covering the behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100