mypy dislikes next() on file objects

When mypy analyzes the following code:

filename = 'some.txt'
with open(filename) as fh:
    c = cast(TextIOWrapper, fh)
    next(c)  # skip line

it yields the following error:
error: No overload variant of "next" matches argument types [io.TextIOWrapper]

Since TextIOWrapper implements the next() method (which is even autocompleted by PyCharm IDE), I would not expect this error to be thrown.

For the moment I make a workaround like this:

fh = cast(TextIOWrapper, open(filename))
fh.__next__()

Navigation Menu