Unexpected "incompatible type" error when chaining bytes(filter())
Nobody has claimed this yet.
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Bug Report
Mypy reports a strange type error when calling bytes(filter(...)) like below.
Write the following contents to a file and run mypy:
f = filter(lambda ch: chr(ch), b"hello")
bytes(f)
bytes(filter(lambda ch: chr(ch), b"hello"))
Mypy reports an error on line 4 but not on lines 1/2, despite the two sections being functionally identical. The expected result is that there should be no errors in this code example.
> mypy /tmp/test.py
/tmp/test.py:4: error: Argument 1 to "chr" has incompatible type "SupportsIndex"; expected "int"
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: mypy 0.931
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: python 3.10.2
- Operating system and version: Arch linux and windows 10
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
Reproduce the report by writing the shown examples to /tmp/test.py and running mypy with no flags. Compare the inferred types for the split and chained forms, then trace the relevant type-checking path; done means both forms produce no errors and the regression is covered by an appropriate test.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100