mypy does not recognize sys.platform with ternary operator
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feature
priority-2-low
topic-ternary-expression
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
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Description
Bug Report
mypy can recognize sys.platform in if cond: ... / else: ... conditions but fails to do it if ternary operator (a if cond else b) is used.
To Reproduce
Consider this piece of code, assuming we are on Linux:
import signal
import sys
signal_type = signal.SIGBREAK if sys.platform == 'win32' else signal.SIGTERM
Expected Behavior
mypy should not raise any error.
Actual Behavior
mypy fails with:
main.py:4: error: Module has no attribute "SIGBREAK"
Found 1 error in 1 file (checked 1 source file)
Environment
- Mypy version used: 0.961
- Python version used: 3.10
- Operating system: Linux
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 running the reported snippet in main.py with mypy on Linux and confirm the SIGBREAK error. Then trace how mypy handles sys.platform checks in ordinary if/else statements versus conditional expressions; done means the ternary form no longer reports the platform-inapplicable attribute error.
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
- 45/100