PEP 604 and line breaks

[srittau]

Describe the style change

Long PEP 604 annotations (X | Y) in function definitions (and probably other contexts) are currently broken into multiple lines without extra indentation. This makes it hard to recognize the arguments in the signature. My suggestion would be to treat those annotations similar to regular bitwise or operators inside type annotations: Indent followup lines and possibly use parentheses.

Examples in the current Black style

def foo(
    i: int,
    x: Loooooooooooooooooooooooong
    | Looooooooooooooooong
    | Looooooooooooooooooooong
    | Looooooong,
    *,
    s: str
) -> None:
    pass

A practical example (with shorter line width):

def create_medical_record_entries(
    context: RequestContext,
    db_entries: Iterable[CharlyMedicalRecordEntry]
    | Iterable[CharlyLabRecordEntry],
    *,
    ignore_signs: bool = True
) -> list[MedicalRecordEntry]:
    ...

Desired style (without extra arguments)

def foo(
    x: (
        Loooooooooooooooooooooooong
        | Looooooooooooooooong
        | Looooooooooooooooooooong
        | Looooooong
    ),
) -> None:
    pass

Or maybe:

def foo(
    x:
        Loooooooooooooooooooooooong
        | Looooooooooooooooong
        | Looooooooooooooooooooong
        | Looooooong,
) -> None:
    pass

Or:

def foo(
    x: Loooooooooooooooooooooooong
        | Looooooooooooooooong
        | Looooooooooooooooooooong
        | Looooooong,
) -> None:
    pass

[srittau]

Options 2 or 3 would only work within function defs, not in variable annotations, though.

[felix-hilden]

To me 1 and 3 look good, 2 is a bit weird. But I agree variable annotations should work similarly.

[srittau]

Option 3 looks clearer to me in function annotations, but I don't know if there should be separate styles for function arguments and other annotations.

[Zeta611]

Current Black line-break is awkward with a short type hinting with a long default value as well:

@app.get("/path/")
async def foo(
    q: str
    | None = Query(None, title="Some long title", description="Some long description")
):
    pass

IMHO the following is better:

@app.get("/path/")
async def foo(
    q: str | None = Query(
        None, title="Some long title", description="Some long description"
    )
):
    pass

It is how it is done without the type annotation.

[MarcDufresne]

Any progress or solution on this? We are facing this issue now that we are switching to Python 3.10.

[ichard26]

None as far as I am aware.