`typing.Protocol` is explicitly treated as not a `type`
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bug
topic-protocols
topic-runtime-semantics
- Dominant language
- Python
- Stars
- 20.6k
- Forks
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Description
Bug Report
At runtime, isinstance(typing.Protocol, type) is True. When type checking, mypy appears to special-case Protocol:
- mypy:
<typing special form> - Pylance/Pyright:
(class) Protocol
To Reproduce
from typing import Protocol
class A(Protocol): pass
assert Protocol in A.__bases__
bases: tuple[type, ...] = (Protocol, *A.__bases__)
Expected Behavior
Same as Pyright, Protocol is a class (type), no errors.
Actual Behavior
main.py:5: error: Non-overlapping container check (element type: "<typing special form>", container item type: "type") [comparison-overlap]
main.py:6: error: Argument 1 to <tuple> has incompatible type "<typing special form>"; expected "type" [arg-type]
Your Environment
- Mypy version used: 1.0.0, 1.10.1, 1.20.2, 2.3.1
- Mypy command-line flags:
--strict - Python version used: 3.6 - 3.14
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 with the provided Python reproduction under mypy --strict and compare its diagnostics with the stated Pyright behavior. Locate mypy's special handling of typing.Protocol, then add or update coverage so Protocol is accepted as a type and the reproduction produces no errors.
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
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 52/100