`x in y` doesn't report errors when `x` is not `str` and `y: union | involving | str`
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bug
topic-union-types
- Dominant language
- Python
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- 20.6k
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Description
Bug Report
This doesn't report an error but can easily crash at runtime:
var: list[int] | str
2 in var
Expected Behavior
var: list[int] | str
2 in var # E: Unsupported operand types for in ("int" and "str") \
# N: Right operand is of type "list[int] | str"
Your Environment
- Mypy version used: 1.0.0-2.1.0
- Mypy command-line flags:
--strict
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the example with mypy under --strict: var: list[int] | str followed by 2 in var. Trace the type-checking path for the in operator and make it report the expected unsupported operand error for the str union member without missing the possible runtime failure.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 62/100