Error using list with union #9555
Description
Bug Report
Given a list of union types, if a list with one of the accepted types in the union is used, mypy throws an error.
I've tried following the link suggested in the error message, but I'm just describing types, no inference, as shown in the docs. Also I'm not sure I understand the issue properly. I've tried searching, but, I didn't find any help, and I'm not sure how to describe it better in order to search, sorry if it was published already.
This behavior was not happening before, we got some new PRs that failed CI because of this recently.
To Reproduce
from typing import List, Union, Dict, Any
names: List[str] = ["mike", "wazowski"]
def what(items: List[Union[str, Dict[str, Any]]]):
...
what(names)Expected Behavior
No error, because List[str] is one of the accepted values of List[Union[str, Dict[str, Any]]]
Actual Behavior
Argument 1 to "what" has incompatible type "List[str]"; expected "List[Union[str, Dict[str, Any]]]"
"List" is invariant -- see http://mypy.readthedocs.io/en/latest/common_issues.html#variance
Your Environment
- Mypy version used:
mypy==0.770
mypy-extensions==0.4.3
- Mypy command-line flags:
mypy src/ - Mypy configuration options from
mypy.ini(and other config files):
[mypy]
files = src, tests
ignore_missing_imports = true
disallow_untyped_decorators = True
disallow_subclassing_any = True
warn_redundant_casts = True
warn_unused_ignores = True
warn_unused_configs = True- Python version used:
3.7.6 - Operating system and version:
Ubuntu 20.04.1 LTS x86_64