Line too long: Lambda with many parameters

[mikelane]

Operating system: macos 10.14.4
Python version: 3.6.7
Black version: 19.3b0
Does also happen on master: Yes

We have an interesting way to create pytest fixtures. We've created a function called lambda_fixture() that lets us skip most of the boilerplate issues when creating fixtures. It looks something like this:

my_user = lambda_fixture(lambda user_factory: user_factory(name='Mike'))

That's all well and good, but sometimes these things can have a pretty long list of parameters. Unfortunately, black doesn't handle this very well:

my_long_variable_name = lambda_fixture(
    lambda fixture_1, another_long_fixture_name, some_fixture_factory, some_long_fixture_name_again, short, wow, long_fixture_name: some_fixture_factory.create_batch(
        size=10,
        something=short,
        something_else=long_fixture_name,
    )
)

It would be nice to have black wrap and/or chop down the lambda parameter list. Bonus points if the indent of the wrap/chop is different than the indent of the body of the lambda.

[zsol]

What formatting do you suggest?

[mikelane]

What formatting do you suggest?

Good question, I should have suggested something. How about this?

my_long_variable_name = lambda_fixture(
    lambda fixture_1, 
           another_long_fixture_name, 
           some_fixture_factory, 
           some_long_fixture_name_again, 
           short, 
           wow, 
           long_fixture_name: 
        some_fixture_factory.create_batch(
            size=10,
            something=short,
            something_else=long_fixture_name,
        )
)

And like regular function params:

my_long_fixture_name_goes_here = lambda_fixture(
    lambda fixture_names, that_take_up, a_lot_of_space, but_not_too_much:
        code_and_stuff.create_batch(goes='here', like='this')
)

[JelleZijlstra]

That would be inconsistent with most of Black's formatting choices because indentation is not a multiple of four. Not that I have a better idea though...

[advance512]

This:

my_long_variable_name = lambda_fixture(
    lambda fixture_1, 
        another_long_fixture_name, 
        some_fixture_factory, 
        some_long_fixture_name_again, 
        short, 
        wow, 
        long_fixture_name: 
            some_fixture_factory.create_batch(
                size=10,
                something=short,
                something_else=long_fixture_name,
            )
)

or even this:

my_long_variable_name = lambda_fixture(
    lambda \
        fixture_1, 
        another_long_fixture_name, 
        some_fixture_factory, 
        some_long_fixture_name_again, 
        short, 
        wow, 
        long_fixture_name: 
            some_fixture_factory.create_batch(
                size=10,
                something=short,
                something_else=long_fixture_name,
            )
)

is definitely better than this:

my_long_variable_name = lambda_fixture(
    lambda fixture_1, another_long_fixture_name, some_fixture_factory, some_long_fixture_name_again, short, wow, long_fixture_name: some_fixture_factory.create_batch(
        size=10,
        something=short,
        something_else=long_fixture_name,
    )
)

This is my idea:

lambda kfjlsdkljfskjfldjsklfd, fdsfsdsdffsdsfd, fsdfsdsfd, sfdfsdsfdsfd,
        dkljsfjlkdsljksdfljksdf, sdfsfdfsfsdsdfsdfdsf, sdfsdffsdfds, sdffsdfdsfds

[hzulla]

If the lambda definition exceeds the maximum line length, this please:

my_long_variable_name = lambda_fixture(
    lambda fixture_1, 
    another_long_fixture_name, 
    some_fixture_factory, 
    some_long_fixture_name_again, 
    short, 
    wow, 
    long_fixture_name: 
        some_fixture_factory.create_batch(
            size=10,
            something=short,
            something_else=long_fixture_name,
        )

Thank you.

[hzulla]

(btw, we were stumbling into this when we wanted to deal with the W0640(cell-var-from-loop) linter warning. An easy remedy to avoid lambda-in-a-loop bugs is changing:

lambda: do_something_with(looped_variable)

into

lambda looped_variable=looped_variable: do_something_with(looped_variable)

But once you want to copy a lot of variables inside a loop to a later lambda-call in that fashion, black will trip over the same issue as the original reporter did here.