The Big Ol' List of Rules

Descriptions and examples for each of the rules in Flake8 (pyflakes, pycodestyle, and mccabe).

Created by Grant McConnaughey. For helpful tips on Python and software development, follow me on Twitter or TinyLetter.

pycodestyle

E101	Indentation contains mixed spaces and tabs
E111	Indentation is not a multiple of four
E112	Expected an indented block
E113	Unexpected indentation
E114	Indentation is not a multiple of four (comment)
E115	Expected an indented block (comment)
E116	Unexpected indentation (comment)
E117	Over-indented
E121	Continuation line under-indented for hanging indent
E122	Continuation line missing indentation or outdented
E123	Closing bracket does not match indentation of opening bracket's line
E124	Closing bracket does not match visual indentation
E125	Continuation line with same indent as next logical line
E126	Continuation line over-indented for hanging indent
E127	Continuation line over-indented for visual indent
E128	Continuation line under-indented for visual indent
E129	Visually indented line with same indent as next logical line
E131	Continuation line unaligned for hanging indent
E133	Closing bracket is missing indentation
E201	Whitespace after '('
E202	Whitespace before ')'
E203	Whitespace before ':'
E211	Whitespace before '('
E221	Multiple spaces before operator
E222	Multiple spaces after operator
E223	Tab before operator
E224	Tab after operator
E225	Missing whitespace around operator
E226	Missing whitespace around arithmetic operator
E227	Missing whitespace around bitwise or shift operator
E228	Missing whitespace around modulo operator
E231	Missing whitespace after ',', ';', or ':'
E241	Multiple spaces after ','
E242	Tab after ','
E251	Unexpected spaces around keyword / parameter equals
E261	At least two spaces before inline comment
E262	Inline comment should start with '# '
E265	Block comment should start with '# '
E266	Too many leading '#' for block comment
E271	Multiple spaces after keyword
E272	Multiple spaces before keyword
E273	Tab after keyword
E274	Tab before keyword
E275	Missing whitespace after keyword
E301	Expected 1 blank line, found 0
E302	Expected 2 blank lines, found 0
E303	Too many blank lines (3)
E304	Blank lines found after function decorator
E305	Expected 2 blank lines after end of function or class
E306	Expected 1 blank line before a nested definition
E401	Multiple imports on one line
E402	Module level import not at top of file
E501	Line too long (82 > 79 characters)
E502	The backslash is redundant between brackets
E701	Multiple statements on one line (colon)
E702	Multiple statements on one line (semicolon)
E703	Statement ends with a semicolon
E704	Multiple statements on one line (def)
E711	Comparison to None should be 'cond is None:'
E712	Comparison to true should be 'if cond is true:' or 'if cond:'
E713	Test for membership should be 'not in'
E714	Test for object identity should be 'is not'
E721	Do not compare types, use 'isinstance()'
E722	Do not use bare except, specify exception instead
E731	Do not assign a lambda expression, use a def
E741	Do not use variables named 'I', 'O', or 'l'
E742	Do not define classes named 'I', 'O', or 'l'
E743	Do not define functions named 'I', 'O', or 'l'
E901	SyntaxError or IndentationError
E902	IOError
E999	SyntaxError
W191	Indentation contains tabs
W291	Trailing whitespace
W292	No newline at end of file
W293	Blank line contains whitespace
W391	Blank line at end of file
W503	Line break occurred before a binary operator
W504	Line break occurred after a binary operator
W601	.has_key() is deprecated, use 'in'
W602	Deprecated form of raising exception
W603	'<>' is deprecated, use '!='
W604	Backticks are deprecated, use 'repr()'
W605	Invalid escape sequence 'x'

pyflakes

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
F901	raise NotImplemented should be raise NotImplementedError

mccabe

C901	Function is too complex