black and flake8 hooks conflicts

Question

Black fail and reformat the following

foo1 = foo2[len(foo3):]

to

foo1 = foo2[len(foo3) :]

But Flake8 fails with

foo1 = foo2[len(foo3) :]

and wants

foo1 = foo2[len(foo3):]

Unless I am mistaken, in this case Flake8 is right.

How to make a pre-commit that doesn't fail with black and flake8, in this case ?

Answer 1

Thanks to the answer of Anthony Sottile we can say that:

1- Black wants extra space for “complex expressions” as foo1 = foo2[len(foo3) :] and this behaviour may raise E203 whitespace before ':' warnings in style guide enforcement tools like Flake8. Since E203 is not PEP 8 compliant, we should tell Flake8 to ignore these warnings.

2- Contrary to what I thought, the pyproject.toml file is not used for the configuration of flake8. We must absolutely and exclusively use .flake8, setup.cfg, or tox.ini.

Finally, here is the configuration that I use (and which fix the issue encountered initially):

$ more .pre-commit-config.yaml
repos:

-   repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.4.0
    hooks: # general hooks
    -   id: check-added-large-files
    -   id: check-ast
    -   id: check-case-conflict
    -   id: check-docstring-first
    -   id: check-json
    -   id: check-merge-conflict
    -   id: check-toml
    -   id: check-xml
    -   id: check-yaml
    -   id: debug-statements
    -   id: end-of-file-fixer
    -   id: fix-encoding-pragma
    -   id: name-tests-test
    -   id: trailing-whitespace

-   repo: https://github.com/psf/black
    rev: 23.1.0
    hooks: # code formatter
    -   id: black
        language: python
        args: ["--line-length=79"]

-   repo: https://github.com/pycqa/isort
    rev: 5.12.0
    hooks: # imports sorting
    -   id: isort
        name: isort (python)

-   repo: https://github.com/econchick/interrogate
    rev: 1.5.0
    hooks: # documentation checker
    -   id: interrogate
        args: [--fail-under=80, -vv]

-   repo: https://github.com/PyCQA/flake8
    rev: 6.0.0
    hooks:
    -   id: flake8
        name: flake8 under python3
        language_version: python3

$ more pyproject.toml
[tool.black]
line-length = 79
include = '\.pyi?$'
exclude = '''
/(
    \.git
  | \.hg
  | \.mypy_cache
  | \.tox
  | \.venv
  | _build
  | buck-out
  | build
  | dist
)/
'''

#[tool.flake8]
#max-line-length = 79
#exclude = [".git", "__pycache__", "dist"]
#extend-ignore = ["E203", "E266", "E501", "W503", "F403", "F401"]
#max-complexity = 10

[tool.isort]
atomic = true
profile = "black"
line_length = 79
skip_gitignore = true

$ more .flake8
[flake8]
ignore = E203, E266, E501, W503, F403, F401
exclude =
    .git,
    __pycache__,
    docs/source/conf.py,
    build,
    dist
max-complexity = 10
max-line-length = 79