Black fails to format complicated f-string

[georgepittock]

Black fails to format complicated f-string

To Reproduce

Black Playground

SUBSCRIPTS = {i: chr(0x2080 + i) for i in range(10)}

def cant_format(row):
    return " + ".join(
                f"{coefficient if coefficient != 1 else ""}x{''.join(SUBSCRIPTS[int(digit)] for digit in str(i+1))}"
                for i, coefficient in enumerate(row)
            )


cant_format([1, 2])

And run it with these arguments:

$ black simplex\utils.py

The resulting error is:

> [cannot format file.py: INTERNAL ERROR: ...](error: cannot format: simplex\utils.py: INTERNAL ERROR: Black produced invalid code: f-string: expecting '}' (<unknown>, line 6). Please report a bug on https://github.com/psf/black/issues.  This invalid output might be helpful: Temp\blk_k8cady1s.log)

Log File Output

  File "src\black\__init__.py", line 1476, in assert_equivalent
  File "src\black\parsing.py", line 140, in parse_ast
SUBSCRIPTS = {i: chr(0x2080 + i) for i in range(10)}


def cant_format(row):
    return " + ".join(
        f"{coefficient if coefficient != 1 else "
        "}x{''.join(SUBSCRIPTS[int(digit)] for digit in str(i+1))}"
        for i, coefficient in enumerate(row)
    )


cant_format([1, 2])

The error is due to the }being carried to the next line. I would expect the whole f-expression to be on one line.

If single quotes are used in the first statement after the else, then black correctly formats this i.e. the below works fine.

SUBSCRIPTS = {i: chr(0x2080 + i) for i in range(10)}

def cant_format(row):
    return " + ".join(
                f"{coefficient if coefficient != 1 else ''}x{''.join(SUBSCRIPTS[int(digit)] for digit in str(i+1))}"
                for i, coefficient in enumerate(row)
            )


cant_format([1, 2])

Expected behaviour

Black should correctly format the code, I would expect something very similar to the following:

SUBSCRIPTS = {i: chr(0x2080 + i) for i in range(10)}


def cant_format(row):
    return " + ".join(
        f"{coefficient if coefficient != 1 else ''}x{''.join(SUBSCRIPTS[int(digit)] for digit in str(i+1))}"
        for i, coefficient in enumerate(row)
    )


cant_format([1, 2])

Environment

>black --version
black, 23.12.1 (compiled: yes)
Python (CPython) 3.12.0

[Lilneo786]

This should work:

SUBSCRIPTS = {i: chr(0x2080 + i) for i in range(10)}

def cant_format(row):
    return " + ".join(
        [
            f"{coefficient if coefficient != 1 else ''}x{''.join(SUBSCRIPTS[int(digit)] for digit in str(i+1))}"
            for i, coefficient in enumerate(row)
        ]
    )

print(cant_format([1, 2]))

[hauntsaninja]

Thanks, duplicate of #3746