False Positive when TypedDict instance used as base __map for new instances?
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Description
Bug Report
Why doesn't mypy accept another TypedDict as the __map argument when defining a new instance as shown below? It seems perfectly valid to me, but I could be missing something.
To Reproduce
Save the following as test_mypy.py and ask mypy to check it:
from typing import TypedDict
class MyTypedDict(TypedDict):
attr1: str
attr2: str
attr3: str
MY_BASE_DICT = MyTypedDict(
attr1="testing",
attr2="typeddict",
attr3="inheritance",
)
new_typed_dict = MyTypedDict(MY_BASE_DICT, attr1="failing")
assert " ".join(new_typed_dict.values()) == "failing typeddict inheritance"
Expected Behavior
> mypy test_mypy.py
Success: no issues found in 1 source file
Actual Behavior
> mypy test_mypy.py
test_mypy.py:17: error: Expected keyword arguments, {...}, or dict(...) in TypedDict constructor [misc]
Found 1 errors in 1 file (checked 1 source file)
Your Environment
- Mypy version used: v1.8.0 (command line call) and v1.6.1 (integrated vscode extension)
- Mypy command-line flags: none required although I'm typically adding
--check-untyped-defs --implicit-optional - Mypy configuration options from
mypy.ini(and other config files): n/a - Python version used: 3.10.6
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 saving the example as test_mypy.py and running mypy test_mypy.py. Trace the TypedDict constructor checking that rejects MY_BASE_DICT, then add a regression test for using a TypedDict instance as the base mapping while retaining keyword overrides. Done means the example passes without the [misc] error.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100