The mypy error is

Need type annotation for "args"  [var-annotated]
Need type annotation for "kwargs"  [var-annotated]

and here is the piece of code

expected_args: Optional[Sequence[Tuple[Any, ...]]]
expected_kwargs: Optional[Sequence[Dict[str, Any]]]

...
expected_args_iter = iter(expected_args or ())
expected_kwargs_iter = iter(expected_kwargs or ())

...
for args, kwargs in itertools.zip_longest(
    expected_args_iter, expected_kwargs_iter, fillvalue={})

Where can I annotate "args" and "kwargs"?

The mypy error is

Need type annotation for "args"  [var-annotated]
Need type annotation for "kwargs"  [var-annotated]

and here is the piece of code

expected_args: Optional[Sequence[Tuple[Any, ...]]]
expected_kwargs: Optional[Sequence[Dict[str, Any]]]

...
expected_args_iter = iter(expected_args or ())
expected_kwargs_iter = iter(expected_kwargs or ())

...
for args, kwargs in itertools.zip_longest(
    expected_args_iter, expected_kwargs_iter, fillvalue={})

Where can I annotate "args" and "kwargs"?

• python
• python-typing
• mypy

• That's really weird... there is no way to annotate the iteration variables of a list comprehension. mypy shouldn't be telling you to do that. (Also None, with a comma is probably not what you want there, but fixing that doesn't make the "Need type annotation" messages go away.) – user2357112 Commented Jan 20 at 7:04
• @user2357112 None, was used to set the default value in function definition. Sorry for the confusion, corrected it in my question. – Sujay Commented Jan 20 at 7:08
• There is no list comprehension in your question, please clarify. There's no way to annotate inside listcomp, but it is possible with regular loop (variables can be annotated anywhere before the loop body). – STerliakov Commented Jan 20 at 23:21

1 Answer 1

This appears to be a bug in mypy v1.14.0. For some reason, any iteration over itertools.zip_longest() with an empty sequence* in fillvalue will cause a similar issue. This is the simplest example I could construct:

import itertools

seq_a: list
seq_b: list

for a, b in itertools.zip_longest(seq_a, seq_b, fillvalue=[]): ...

This is specific to both mypy and empty sequences. Non-empty sequences, non-sequences, and using Pyright are all fine.

In your particular case, you can work around this issue by leaving fillvalue as its default (None) and hard-coding an exception into your comprehension.

pretty_unused_args = [
    ', '.join(itertools.chain(
        (repr(a) for a in args) if args is not None else [],
        ('%s=%r' % kwarg for kwarg in kwargs.items()) if kwargs is not None else []))
    for args, kwargs in itertools.zip_longest(
        expected_args_iter, expected_kwargs_iter)
]

_{*Besides (), but including tuple()}