Introduction

pep8 is a tool to check your Python code against some of the style conventions in PEP 8.

Features

  • Plugin architecture: Adding new checks is easy.
  • Parseable output: Jump to error location in your editor.
  • Small: Just one Python file, requires only stdlib. You can use just the pep8.py file for this purpose.
  • Comes with a comprehensive test suite.

Disclaimer

This utility does not enforce every single rule of PEP 8. It helps to verify that some coding conventions are applied but it does not intend to be exhaustive. Some rules cannot be expressed with a simple algorithm, and other rules are only guidelines which you could circumvent when you need to.

Always remember this statement from PEP 8:

A style guide is about consistency. Consistency with this style guide is important. Consistency within a project is more important. Consistency within one module or function is most important.

Among other things, these features are currently not in the scope of the pep8 library:

  • naming conventions: this kind of feature is supported through plugins. Install flake8 and the pep8-naming extension to use this feature.
  • docstring conventions: they are not in the scope of this library; see the pep257 project.
  • automatic fixing: see the section PEP8 Fixers in the related tools page.

Installation

You can install, upgrade, uninstall pep8.py with these commands:

$ pip install pep8
$ pip install --upgrade pep8
$ pip uninstall pep8

There’s also a package for Debian/Ubuntu, but it’s not always the latest version:

$ sudo apt-get install pep8

Example usage and output

$ pep8 --first optparse.py
optparse.py:69:11: E401 multiple imports on one line
optparse.py:77:1: E302 expected 2 blank lines, found 1
optparse.py:88:5: E301 expected 1 blank line, found 0
optparse.py:222:34: W602 deprecated form of raising exception
optparse.py:347:31: E211 whitespace before '('
optparse.py:357:17: E201 whitespace after '{'
optparse.py:472:29: E221 multiple spaces before operator
optparse.py:544:21: W601 .has_key() is deprecated, use 'in'

You can also make pep8.py show the source code for each error, and even the relevant text from PEP 8:

$ pep8 --show-source --show-pep8 testsuite/E40.py
testsuite/E40.py:2:10: E401 multiple imports on one line
import os, sys
         ^
    Imports should usually be on separate lines.

    Okay: import os\nimport sys
    E401: import sys, os

Or you can display how often each error was found:

$ pep8 --statistics -qq Python-2.5/Lib
232     E201 whitespace after '['
599     E202 whitespace before ')'
631     E203 whitespace before ','
842     E211 whitespace before '('
2531    E221 multiple spaces before operator
4473    E301 expected 1 blank line, found 0
4006    E302 expected 2 blank lines, found 1
165     E303 too many blank lines (4)
325     E401 multiple imports on one line
3615    E501 line too long (82 characters)
612     W601 .has_key() is deprecated, use 'in'
1188    W602 deprecated form of raising exception

Quick help is available on the command line:

$ pep8 -h
Usage: pep8 [options] input ...

Options:
  --version            show program's version number and exit
  -h, --help           show this help message and exit
  -v, --verbose        print status messages, or debug with -vv
  -q, --quiet          report only file names, or nothing with -qq
  --first              show first occurrence of each error
  --exclude=patterns   exclude files or directories which match these comma
                       separated patterns (default: .svn,CVS,.bzr,.hg,.git)
  --filename=patterns  when parsing directories, only check filenames matching
                       these comma separated patterns (default: *.py)
  --select=errors      select errors and warnings (e.g. E,W6)
  --ignore=errors      skip errors and warnings (e.g. E4,W)
  --show-source        show source code for each error
  --show-pep8          show text of PEP 8 for each error (implies --first)
  --statistics         count errors and warnings
  --count              print total number of errors and warnings to standard
                       error and set exit code to 1 if total is not null
  --max-line-length=n  set maximum allowed line length (default: 79)
  --hang-closing       hang closing bracket instead of matching indentation of
                       opening bracket's line
  --format=format      set the error format [default|pylint|<custom>]
  --diff               report only lines changed according to the unified diff
                       received on STDIN

  Testing Options:
    --benchmark        measure processing speed

  Configuration:
    The project options are read from the [pep8] section of the tox.ini
    file or the setup.cfg file located in any parent folder of the path(s)
    being processed.  Allowed options are: exclude, filename, select,
    ignore, max-line-length, hang-closing, count, format, quiet, show-pep8,
    show-source, statistics, verbose.

    --config=path      user config file location (default: ~/.config/pep8)

Configuration

The behaviour may be configured at two levels.

The user settings are read from the ~/.config/pep8 file. Example:

[pep8]
ignore = E226,E302,E41
max-line-length = 160

At the project level, a tox.ini file or a setup.cfg file is read if present (.pep8 file is also supported, but it is deprecated). If none of these files have a [pep8] section, no project specific configuration is loaded.

If the ignore option is not in the configuration and not in the arguments, only the error codes E123/E133, E226 and E241/E242 are ignored (see below).

Error codes

This is the current list of error and warning codes:

code sample message
E1 Indentation
E101 indentation contains mixed spaces and tabs
E111 indentation is not a multiple of four
E112 expected an indented block
E113 unexpected indentation
   
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
   
E2 Whitespace
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 ‘,’
   
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 ‘# ‘
   
E271 multiple spaces after keyword
E272 multiple spaces before keyword
E273 tab after keyword
E274 tab before keyword
   
E3 Blank line
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
   
E4 Import
E401 multiple imports on one line
   
E5 Line length
E501 (^) line too long (82 > 79 characters)
E502 the backslash is redundant between brackets
   
E7 Statement
E701 multiple statements on one line (colon)
E702 multiple statements on one line (semicolon)
E703 statement ends with a semicolon
E711 (^) comparison to None should be ‘if 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()’
   
E9 Runtime
E901 SyntaxError or IndentationError
E902 IOError
   
W1 Indentation warning
W191 indentation contains tabs
   
W2 Whitespace warning
W291 trailing whitespace
W292 no newline at end of file
W293 blank line contains whitespace
   
W3 Blank line warning
W391 blank line at end of file
   
W6 Deprecation warning
W601 .has_key() is deprecated, use ‘in’
W602 deprecated form of raising exception
W603 ‘<>’ is deprecated, use ‘!=’
W604 backticks are deprecated, use ‘repr()’

(*) In the default configuration, the checks E123, E133, E226, E241 and E242 are ignored because they are not rules unanimously accepted, and PEP 8 does not enforce them. The check E133 is mutually exclusive with check E123. Use switch --hang-closing to report E133 instead of E123.

(^) These checks can be disabled at the line level using the # noqa special comment. This possibility should be reserved for special cases.

Special cases aren’t special enough to break the rules.

Note: most errors can be listed with such one-liner:

$ python pep8.py --first --select E,W testsuite/ --format '%(code)s: %(text)s'