Skip to content

E203: False positive "whitespace before ':' " on list slice. #373

Description

@aleksey-kutepov

I've encountered the problem in the following code:

a = [1, 2, 3, 4, 5]
b = a[1+1 : 2+2]  # E203
c = a[1 + 1 : 2 + 2]  # E203
d = a[1+1:2+2]

However, PEP8 chapter https://www.python.org/dev/peps/pep-0008/#whitespace-in-expressions-and-statements handles this as good style:

However, in a slice the colon acts like a binary operator, and should have equal amounts on either side (treating it as the operator with the lowest priority). In an extended slice, both colons must have the same amount of spacing applied. Exception: when a slice parameter is omitted, the space is omitted.

Yes:

ham[1:9], ham[1:9:3], ham[:9:3], ham[1::3], ham[1:9:]
ham[lower:upper], ham[lower:upper:], ham[lower::step]
ham[lower+offset : upper+offset]
ham[: upper_fn(x) : step_fn(x)], ham[:: step_fn(x)]
ham[lower + offset : upper + offset]
No:

ham[lower + offset:upper + offset]
ham[1: 9], ham[1 :9], ham[1:9 :3]
ham[lower : : upper]
ham[ : upper]

Activity

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

No one assigned

    Type

    No type

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions