DefaultDict Typing is Overly Strict

[blink1073]

The docs for defaultdict say:

The first argument provides the initial value for the default_factory attribute; it defaults to None. All remaining arguments are treated the same as if they were passed to the dict constructor, including keyword arguments.

However, the second argument is currently treated as a generic type that influences the type of the first argument.

The following should be valid:

>>> dict([('foo', 'bar')])
{'foo': 'bar'}
>>> dct = collections.defaultdict(dict, [('foo', 'bar')])
>>> dct
defaultdict(<class 'dict'>, {'foo': 'bar'})
>>> dct['g']
{}
>>> dct
defaultdict(<class 'dict'>, {'foo': 'bar', 'g': {}})

However, we get the error error: Argument 1 to "defaultdict" has incompatible type "Type[Dict[Any, Any]]"; expected "Optional[Callable[[], str]]".

[AlexWaygood]

It works fine as long as you give it an explicit annotation:

from collections import defaultdict
from typing import Any

dct: defaultdict[str, str | dict[Any, Any]] = defaultdict(dict, [('foo', 'bar')])

<=3.8 compatible version, if you're not using from __future__ import annotations:

from collections import defaultdict
from typing import Any, DefaultDict, Dict, Union

dct: DefaultDict[str, Union[str, Dict[Any, Any]]] = defaultdict(dict, [('foo', 'bar')])

[blink1073]

Makes sense, thanks @AlexWaygood!

[AlexWaygood]

Makes sense, thanks @AlexWaygood!

No worries, happy typing!