`typing.TypeAliasType` cannot be used to declare self-referential types
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bug
topic-pep-695
topic-recursive-types
- Dominant language
- Python
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- 20.6k
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Description
Bug Report, To Reproduce, & Actual Behaviour
See mypy Playground:
type T = dict[str, "T"] # OK
from typing import TypeAliasType
T2 = TypeAliasType("T2", dict[str, "T2"]) # E: Cannot resolve name "T2" (possible cyclic definition) [misc]
Expected Behavior
Self-referential type successfully declared
Your Environment
- Mypy version used: 1.13.0
- Mypy command-line flags: (none)
- Mypy configuration options from
mypy.ini(and other config files): (none) - Python version used: 3.12
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 reported diagnostic in the linked mypy Playground using Python 3.12 and the TypeAliasType example. Trace how mypy resolves the quoted self-reference in the TypeAliasType form, then verify that the example is accepted without regressing the equivalent type statement.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers, devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100