Error / Violation Codes

Flake8 and its plugins assign a code to each message that we refer to as a error code (or violation). Most plugins will list their error codes in their documentation or README.

Flake8 installs pycodestyle, pyflakes, and mccabe by default and generates its own error codes for pyflakes:

Code	Example Message
F401	module imported but unused
F402	import module from line N shadowed by loop variable
F403	‘from module import *’ used; unable to detect undefined names
F404	future import(s) name after other statements
F405	name may be undefined, or defined from star imports: module
F811	redefinition of unused name from line N
F812	list comprehension redefines name from line N
F821	undefined name name
F822	undefined name name in __all__
F823	local variable name ... referenced before assignment
F831	duplicate argument name in function definition
F841	local variable name is assigned to but never used

mccabe only ever reports one violation - C901 based on the complexity value provided by the user.

Users should also reference pycodestyle’s list of error codes.