[style] Function default parameters - ugly lambda explosion

[Starwort]

Describe the style change

Lambdas used as default parameters for functions look really ugly when the function parameter is exploded (e.g. via a typehint being too long

Examples in the current Black style

class Foo:
    def bar(
        self,
        baz: typing.Callable[
            # long typevar name (and this comment) causes
            # declaration to be exploded
            [SpecialisationT, SpecialisationT], SpecialisationT
        ] = lambda i, j: j
        - i,  # ugly line split here
    ):
        ...

Desired style

class Foo:
    def bar(
        self,
        baz: typing.Callable[
            [SpecialisationT, SpecialisationT], SpecialisationT
        ] = lambda i, j: j - i,  # no ugly line split
    ):
        ...

Additional context

The formatting issue can be sidestepped with a pair of brackets around the lambda, so not top priority, but this is uncharacteristically bad formatting

[felix-hilden]

All for it. And I'd like to see the lambda on a separate line depending on which element violates the line length first. (playground examples)

typing.Callable[
    ReallyStupidlyLongTypeVariableThatIsPracticallyNeverendingAndGoesOverLineLenght
] = (lambda i, j: j - i)
# parens prolly useless above too

typing.Callable[ReallyStupidlyLongTypeVariableThatIsPracticallyNeverending] = (
    lambda i, j: j - i
)

def bar(
    baz: typing.Callable[QuiteLengthyTypeVariable] = (
        lambda withmuchlonger, argumentnameshere: withmuchlonger - argumentnameshere
    ),
):
    ...