PEP 8: E203 (whitespace before :) violation

[shifqu]

Black violates PEP 8: E203 whitespace before ':' when using a method call as first slicing index

Steps to reproduce the behavior:

Playground Link

# Method call used in subsetting --> Unexpected behaviour
foo = "bar"
foo[foo.find("a") :]  # PEP 8 E203 whitespace before :

# Variable used in subsetting --> Expected behaviour
foo = "bar"
a_index = foo.find("a")
foo[a_index:]

# Value used in subsetting --> Expected behaviour
foo = "bar"
a_index = foo.find("a")
foo[1:]

Expected behavior

foo = "bar"
foo[foo.find("a"):]  # No whitespace after first slicing index

Environment (please complete the following information):

• Version: stable [version 20.8b1]
• OS and Python version: MacOs Catalina v10.15.7/Python 3.8.6

Does this bug also happen on master?

Yes, Playground Link

[iago-lito]

This is expected behaviour (also I think an issue heavily duplicated in this repo e.g. #280 #354 #373 #565 #889 #940 #1343 #1413).

https://black.readthedocs.io/en/stable/the_black_code_style.html#slices

[shifqu]

Oh, did not find this is in the docs. Thanks for the information!