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Flake8 Python linter

Version 7.4.1 · source

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Start here

flake8
Lint the current directory
flake8 <file.py>
Lint one file
flake8 --show-source
Show the offending line
flake8 --select=E,F
Only errors and pyflakes
flake8 --extend-ignore=<code>
Skip a rule
flake8 --max-line-length=100
Allow longer lines
flake8 --statistics -qq
Count by code
flake8 --version
Version and plugins

Concepts

  1. Python files found by path
  2. Plugins E W F C90 + extras
  3. select / ignore config + CLI + noqa
  4. Output exit 1 if any

Run

flake8
Check all Python files here
flake8 <path> ...
Check files or directories
flake8 -
Read source from stdin
flake8 --stdin-display-name <name> -
Name to show for stdin input
flake8 --version
Show versions of flake8 and plugins
flake8 --count
Print total number of violations
flake8 -q
Print only file names with errors
flake8 -qq
Print nothing, just set the exit code
flake8 --exit-zero
Always exit 0 despite violations
flake8 -j <n>
Number of parallel jobs
flake8 --color never
Disable coloured output

Output

flake8 --show-source
Print the offending source line
flake8 --statistics
Count violations per code
flake8 --format=pylint
Pylint-style output
flake8 --format='%(path)s:%(row)d %(code)s'
Custom format string
Keys: path, row, col, code, text.
flake8 --output-file <file>
Write report to a file
flake8 --tee --output-file <file>
Write to file and stdout
flake8 --benchmark
Print timing information
flake8 --bug-report
Dump versions and config as JSON

Select and ignore

flake8 --select=<codes>
Report only these codes or prefixes
Replaces the default set; plugin codes you leave out are silenced.
flake8 --extend-select=<codes>
Add codes to the default selection
flake8 --ignore=<codes>
Replace the default ignore list
Dropping the defaults (E121,E123,E126,E226,E24,E704,W503,W504) turns those checks on.
flake8 --extend-ignore=<codes>
Ignore more codes, keep the defaults
flake8 --per-file-ignores='<glob>:<codes>'
Ignore codes for matching files
flake8 --disable-noqa
Report even lines with # noqa
flake8 --max-complexity=<n>
Enable C901 above this complexity
Off by default; 10 is a common starting point.
flake8 --max-line-length=<n>
Line length limit for E501
flake8 --max-doc-length=<n>
Limit comments and docstrings (W505)
flake8 --indent-size=<n>
Indentation width, default 4
flake8 --hang-closing
Expect hanging closing brackets
flake8 --doctests
Also check syntax in doctests
flake8 --builtins=<names>
Extra names F821 should accept

Files

flake8 --exclude=<patterns>
Replace the default exclude list
flake8 --extend-exclude=<patterns>
Skip more paths, keep defaults
flake8 --filename=<patterns>
Which file names to check (default *.py)
git diff --name-only -- '*.py' | xargs flake8
Lint only changed files

Inline control

# noqa
Silence all codes on this line
# noqa: <code>[, <code>]
Silence only these codes on this line
Always name the code; a bare noqa hides real problems.
# flake8: noqa
Skip the whole file (own line)
With codes, as '# flake8: noqa: E123', it silences those codes file-wide.

Config

flake8 --config <file>
Use only this config file
flake8 --append-config <file>
Read an extra config file last
flake8 --isolated
Ignore all config files
flake8 --require-plugins=<names>
Fail if a plugin is missing
flake8 --enable-extensions=<codes>
Turn on off-by-default plugins
flake8 -v
Show which config and plugins load

Common codes

Frequent codes
Code Meaning
E501 line too long
E302 expected 2 blank lines
E231 missing whitespace after ','
E203 whitespace before ':'
W291 trailing whitespace
W605 invalid escape sequence
F401 imported but unused
F841 local variable assigned, never used
F821 undefined name
E722 bare except
E741 ambiguous variable name
C901 function too complex
Code prefixes
Prefix Source
E1-E7 pycodestyle errors
W pycodestyle warnings
F pyflakes
C90 mccabe

Recipes

setup.cfg / .flake8
[flake8]max-line-length = 100extend-ignore = E203per-file-ignores =    __init__.py: F401    tests/*: S101exclude = .git,build,.venv
With Black
# Black-compatible settings[flake8]max-line-length = 88extend-ignore = E203,E701
CI: hard errors then advice
flake8 --count --select=E9,F63,F7,F82 --show-source --statisticsflake8 --count --exit-zero --max-complexity=10 --statistics
Pre-commit hook
# .pre-commit-config.yamlrepos:  - repo: https://github.com/PyCQA/flake8    rev: 7.4.1    hooks:      - id: flake8