Regression in 1.7: mypy loses truthiness constraint for union containing tuple
Open
Nobody has claimed this yet.
bug
topic-type-narrowing
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
def f(x: bool | tuple[int, int]):
if x:
if x is True or x[0]:
pass
Gives:
main.py:3: error: Value of type "Literal[False] | tuple[int, int]" is not indexable [index]
This error is newly reported after #16237
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 supplied example with mypy and compare the behavior introduced after issue #16237. Trace the narrowing logic for a truthiness check on a union of bool and tuple. Done means the example no longer reports an indexability error while preserving correct narrowing for the other branches.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100