Black: [Critical] Black violates pep8 (E203)

[DhiaTN]

Operating system: MacOS
Python version: 3.6
Black version: 18.9b0
Does also happen on master: yes

Black is violating pep8 rules while formatting, it's introducing spaces in list slices:

x/api.py:28:47: E203 whitespace before ':'
y/api.py:28:52: E203 whitespace before ':'
2     E203 whitespace before ':'

• Original code:
  l = [i.name for i in x[_offset: _offset + _limit]]

• Transformed code:
  l = [i.name for i in x[_offset : _offset + _limit]]

[cas--]

I believe this is correct for slicing:

See https://github.com/ambv/black/issues/280 and https://github.com/PyCQA/pycodestyle/issues/373

[JelleZijlstra]

Indeed. This is also documented in https://github.com/ambv/black#slices.