"Cannot determine type" error in `__init__` when argument has the same type as the class and accessing attribute before it's defined
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bug
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
from __future__ import annotations
from typing import reveal_type
class Foo:
def __init__(self, value: Foo | None = None):
if value:
reveal_type(value.parent) # Cannot determine type of "parent"
self.parent = value
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 example in the linked mypy playground, focusing on the access to value.parent before self.parent is assigned. Trace the type checker's handling of this self-referential init case and verify that the erroneous "Cannot determine type" diagnostic is gone while the attribute receives the expected inferred type.
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
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100