List comprehension with TypedDict fails type checking
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bug
topic-typed-dict
- Dominant language
- Python
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Description
Bug Report
(A clear and concise description of what the bug is.)
To Reproduce
I've made a file t.py:
from typing import TypedDict, List
class Dct(TypedDict):
x: int
def foo() -> List[Dct]:
return [item for item in [{"x": 3}]]
Expected Behavior
(Write what you thought would happen.)
Without the list comprehension, it works fine:
from typing import TypedDict, List
class Dct(TypedDict):
x: int
def foo() -> List[Dct]:
return [{"x": 3}]
Actual Behavior
$ mypy t.py
t.py:9: error: List comprehension has incompatible type List[Dict[str, int]]; expected List[Dct] [misc]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: mypy 0.812
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files): - Python version used: 3.8.8
- Operating system and version:
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 report with the provided t.py example and mypy 0.812, comparing the list-comprehension result with the direct list return. Trace the type-checking path for list comprehensions and TypedDict values; done means the comprehension is accepted as List[Dct] without regressing related checks.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100