Developer’s notes

Source code

The source code is currently available on GitHub under the terms and conditions of the Expat license. Fork away!

Direction

Some high-level aims and directions to bear in mind for contributions:

  • pep8 is intended to be as fast as possible. Using the ast module defeats that purpose. The pep8-naming plugin exists for this sort of functionality.
  • If you want to provide extensibility / plugins, please see flake8 - pep8 doesn’t want or need a plugin architecture.
  • Python 2.6 support is still deemed important.
  • pep8 aims to have no external dependencies.

Contribute

You can add checks to this program by writing plugins. Each plugin is a simple function that is called for each line of source code, either physical or logical.

Physical line:

  • Raw line of text from the input file.

Logical line:

  • Multi-line statements converted to a single line.
  • Stripped left and right.
  • Contents of strings replaced with "xxx" of same length.
  • Comments removed.

The check function requests physical or logical lines by the name of the first argument:

def maximum_line_length(physical_line)
def extraneous_whitespace(logical_line)
def blank_lines(logical_line, blank_lines, indent_level, line_number)

The last example above demonstrates how check plugins can request additional information with extra arguments. All attributes of the Checker object are available. Some examples:

  • lines: a list of the raw lines from the input file
  • tokens: the tokens that contribute to this logical line
  • line_number: line number in the input file
  • total_lines: number of lines in the input file
  • blank_lines: blank lines before this one
  • indent_char: indentation character in this file (" " or "\t")
  • indent_level: indentation (with tabs expanded to multiples of 8)
  • previous_indent_level: indentation on previous line
  • previous_logical: previous logical line

Check plugins can also maintain per-file state. If you need this, declare a parameter named checker_state. You will be passed a dict, which will be the same one for all lines in the same file but a different one for different files. Each check plugin gets its own dict, so you don’t need to worry about clobbering the state of other plugins.

The docstring of each check function shall be the relevant part of text from PEP 8. It is printed if the user enables --show-pep8. Several docstrings contain examples directly from the PEP 8 document.

Okay: spam(ham[1], {eggs: 2})
E201: spam( ham[1], {eggs: 2})

These examples are verified automatically when pep8.py is run with the --doctest option. You can add examples for your own check functions. The format is simple: "Okay" or error/warning code followed by colon and space, the rest of the line is example source code. If you put 'r' before the docstring, you can use \n for newline and \t for tab.

Then be sure to pass the tests:

$ python pep8.py --testsuite testsuite
$ python pep8.py --doctest
$ python pep8.py --verbose pep8.py

Changes

1.7.1 (2017-10-22)

Changes:

  • Prominently note via warning message that the tool is no longer released as pep8 and will only be fixed in the pycodestyle package

1.7.0 (2016-01-12)

Announcements:

Changes:

  • Reverted the fix in #368, “options passed on command line are only ones accepted” feature. This has many unintended consequences in pep8 and flake8 and needs to be reworked when I have more time.
  • Added support for Python 3.5. (Issue #420 & #459)
  • Added support for multi-line config_file option parsing. (Issue #429)
  • Improved parameter parsing. (Issues #420 & #456)

Bugs:

  • Fixed BytesWarning on Python 3. (Issue #459)

1.6.2 (2015-02-15)

Changes:

  • Added check for breaking around a binary operator. (Issue #197, Pull #305)

Bugs:

  • Restored config_file parameter in process_options(). (Issue #380)

1.6.1 (2015-02-08)

Changes:

  • Assign variables before referenced. (Issue #287)

Bugs:

  • Exception thrown due to unassigned local_dir variable. (Issue #377)

1.6.0 (2015-02-06)

News:

Changes:

  • Report E731 for lambda assignment. (Issue #277)
  • Report E704 for one-liner def instead of E701. Do not report this error in the default configuration. (Issue #277)
  • Replace codes E111, E112 and E113 with codes E114, E115 and E116 for bad indentation of comments. (Issue #274)
  • Report E266 instead of E265 when the block comment starts with multiple #. (Issue #270)
  • Report E402 for import statements not at the top of the file. (Issue #264)
  • Do not enforce whitespaces around ** operator. (Issue #292)
  • Strip whitespace from around paths during normalization. (Issue #339 / #343)
  • Update --format documentation. (Issue #198 / Pull Request #310)
  • Add .tox/ to default excludes. (Issue #335)
  • Do not report E121 or E126 in the default configuration. (Issues #256 / #316)
  • Allow spaces around the equals sign in an annotated function. (Issue #357)
  • Allow trailing backslash if in an inline comment. (Issue #374)
  • If --config is used, only that configuration is processed. Otherwise, merge the user and local configurations are merged. (Issue #368 / #369)

Bug fixes:

  • Don’t crash if Checker.build_tokens_line() returns None. (Issue #306)
  • Don’t crash if os.path.expanduser() throws an ImportError. (Issue #297)
  • Missing space around keyword parameter equal not always reported, E251. (Issue #323)
  • Fix false positive E711/E712/E713. (Issues #330 and #336)
  • Do not skip physical checks if the newline is escaped. (Issue #319)
  • Flush sys.stdout to avoid race conditions with printing. See flake8 bug: https://gitlab.com/pycqa/flake8/issues/17 for more details. (Issue #363)

1.5.7 (2014-05-29)

Bug fixes:

  • Skip the traceback on “Broken pipe” signal. (Issue #275)
  • Do not exit when an option in setup.cfg or tox.ini is not recognized.
  • Check the last line even if it does not end with a newline. (Issue #286)
  • Always open files in universal newlines mode in Python 2. (Issue #288)

1.5.6 (2014-04-14)

Bug fixes:

  • Check the last line even if it has no end-of-line. (Issue #273)

1.5.5 (2014-04-10)

Bug fixes:

  • Fix regression with E22 checks and inline comments. (Issue #271)

1.5.4 (2014-04-07)

Bug fixes:

  • Fix negative offset with E303 before a multi-line docstring. (Issue #269)

1.5.3 (2014-04-04)

Bug fixes:

  • Fix wrong offset computation when error is on the last char of a physical line. (Issue #268)

1.5.2 (2014-04-04)

Changes:

  • Distribute a universal wheel file.

Bug fixes:

  • Report correct line number for E303 with comments. (Issue #60)
  • Do not allow newline after parameter equal. (Issue #252)
  • Fix line number reported for multi-line strings. (Issue #220)
  • Fix false positive E121/E126 with multi-line strings. (Issue #265)
  • Fix E501 not detected in comments with Python 2.5.
  • Fix caret position with --show-source when line contains tabs.

1.5.1 (2014-03-27)

Bug fixes:

  • Fix a crash with E125 on multi-line strings. (Issue #263)

1.5 (2014-03-26)

Changes:

  • Report E129 instead of E125 for visually indented line with same indent as next logical line. (Issue #126)
  • Report E265 for space before block comment. (Issue #190)
  • Report E713 and E714 when operators not in and is not are recommended. (Issue #236)
  • Allow long lines in multiline strings and comments if they cannot be wrapped. (Issue #224).
  • Optionally disable physical line checks inside multiline strings, using # noqa. (Issue #242)
  • Change text for E121 to report “continuation line under-indented for hanging indent” instead of indentation not being a multiple of 4.
  • Report E131 instead of E121 / E126 if the hanging indent is not consistent within the same continuation block. It helps when error E121 or E126 is in the ignore list.
  • Report E126 instead of E121 when the continuation line is hanging with extra indentation, even if indentation is not a multiple of 4.

Bug fixes:

  • Allow the checkers to report errors on empty files. (Issue #240)
  • Fix ignoring too many checks when --select is used with codes declared in a flake8 extension. (Issue #216)
  • Fix regression with multiple brackets. (Issue #214)
  • Fix StyleGuide to parse the local configuration if the keyword argument paths is specified. (Issue #246)
  • Fix a false positive E124 for hanging indent. (Issue #254)
  • Fix a false positive E126 with embedded colon. (Issue #144)
  • Fix a false positive E126 when indenting with tabs. (Issue #204)
  • Fix behaviour when exclude is in the configuration file and the current directory is not the project directory. (Issue #247)
  • The logical checks can return None instead of an empty iterator. (Issue #250)
  • Do not report multiple E101 if only the first indentation starts with a tab. (Issue #237)
  • Fix a rare false positive W602. (Issue #34)

1.4.6 (2013-07-02)

Changes:

  • Honor # noqa for errors E711 and E712. (Issue #180)
  • When both a tox.ini and a setup.cfg are present in the project directory, merge their contents. The tox.ini file takes precedence (same as before). (Issue #182)
  • Give priority to --select over --ignore. (Issue #188)
  • Compare full path when excluding a file. (Issue #186)
  • New option --hang-closing to switch to the alternative style of closing bracket indentation for hanging indent. Add error E133 for closing bracket which is missing indentation. (Issue #103)
  • Accept both styles of closing bracket indentation for hanging indent. Do not report error E123 in the default configuration. (Issue #103)

Bug fixes:

  • Do not crash when running AST checks and the document contains null bytes. (Issue #184)
  • Correctly report other E12 errors when E123 is ignored. (Issue #103)
  • Fix false positive E261/E262 when the file contains a BOM. (Issue #193)
  • Fix E701, E702 and E703 not detected sometimes. (Issue #196)
  • Fix E122 not detected in some cases. (Issue #201 and #208)
  • Fix false positive E121 with multiple brackets. (Issue #203)

1.4.5 (2013-03-06)

  • When no path is specified, do not try to read from stdin. The feature was added in 1.4.3, but it is not supported on Windows. Use - filename argument to read from stdin. This usage is supported since 1.3.4. (Issue #170)
  • Do not require setuptools in setup.py. It works around an issue with pip and Python 3. (Issue #172)
  • Add __pycache__ to the ignore list.
  • Change misleading message for E251. (Issue #171)
  • Do not report false E302 when the source file has a coding cookie or a comment on the first line. (Issue #174)
  • Reorganize the tests and add tests for the API and for the command line usage and options. (Issues #161 and #162)
  • Ignore all checks which are not explicitly selected when select is passed to the StyleGuide constructor.

1.4.4 (2013-02-24)

  • Report E227 or E228 instead of E225 for whitespace around bitwise, shift or modulo operators. (Issue #166)
  • Change the message for E226 to make clear that it is about arithmetic operators.
  • Fix a false positive E128 for continuation line indentation with tabs.
  • Fix regression with the --diff option. (Issue #169)
  • Fix the TestReport class to print the unexpected warnings and errors.

1.4.3 (2013-02-22)

  • Hide the --doctest and --testsuite options when installed.
  • Fix crash with AST checkers when the syntax is invalid. (Issue #160)
  • Read from standard input if no path is specified.
  • Initiate a graceful shutdown on Control+C.
  • Allow to change the checker_class for the StyleGuide.

1.4.2 (2013-02-10)

  • Support AST checkers provided by third-party applications.
  • Register new checkers with register_check(func_or_cls, codes).
  • Allow to construct a StyleGuide with a custom parser.
  • Accept visual indentation without parenthesis after the if statement. (Issue #151)
  • Fix UnboundLocalError when using # noqa with continued lines. (Issue #158)
  • Re-order the lines for the StandardReport.
  • Expand tabs when checking E12 continuation lines. (Issue #155)
  • Refactor the testing class TestReport and the specific test functions into a separate test module.

1.4.1 (2013-01-18)

  • Allow sphinx.ext.autodoc syntax for comments. (Issue #110)
  • Report E703 instead of E702 for the trailing semicolon. (Issue #117)
  • Honor # noqa in addition to # nopep8. (Issue #149)
  • Expose the OptionParser factory for better extensibility.

1.4 (2012-12-22)

  • Report E226 instead of E225 for optional whitespace around common operators (*, **, /, + and -). This new error code is ignored in the default configuration because PEP 8 recommends to “use your own judgement”. (Issue #96)
  • Lines with a # nopep8 at the end will not issue errors on line length E501 or continuation line indentation E12*. (Issue #27)
  • Fix AssertionError when the source file contains an invalid line ending "\r\r\n". (Issue #119)
  • Read the [pep8] section of tox.ini or setup.cfg if present. (Issue #93 and #141)
  • Add the Sphinx-based documentation, and publish it on http://pep8.readthedocs.org/. (Issue #105)

1.3.4 (2012-12-18)

  • Fix false positive E124 and E128 with comments. (Issue #100)
  • Fix error on stdin when running with bpython. (Issue #101)
  • Fix false positive E401. (Issue #104)
  • Report E231 for nested dictionary in list. (Issue #142)
  • Catch E271 at the beginning of the line. (Issue #133)
  • Fix false positive E126 for multi-line comments. (Issue #138)
  • Fix false positive E221 when operator is preceded by a comma. (Issue #135)
  • Fix --diff failing on one-line hunk. (Issue #137)
  • Fix the --exclude switch for directory paths. (Issue #111)
  • Use - filename to read from standard input. (Issue #128)

1.3.3 (2012-06-27)

  • Fix regression with continuation line checker. (Issue #98)

1.3.2 (2012-06-26)

  • Revert to the previous behaviour for --show-pep8: do not imply --first. (Issue #89)
  • Add E902 for IO errors. (Issue #87)
  • Fix false positive for E121, and missed E124. (Issue #92)
  • Set a sensible default path for config file on Windows. (Issue #95)
  • Allow verbose in the configuration file. (Issue #91)
  • Show the enforced max-line-length in the error message. (Issue #86)

1.3.1 (2012-06-18)

  • Explain which configuration options are expected. Accept and recommend the options names with hyphen instead of underscore. (Issue #82)
  • Do not read the user configuration when used as a module (except if config_file=True is passed to the StyleGuide constructor).
  • Fix wrong or missing cases for the E12 series.
  • Fix cases where E122 was missed. (Issue #81)

1.3 (2012-06-15)

Warning

The internal API is backwards incompatible.

  • Remove global configuration and refactor the library around a StyleGuide class; add the ability to configure various reporters. (Issue #35 and #66)
  • Read user configuration from ~/.config/pep8 and local configuration from ./.pep8. (Issue #22)
  • Fix E502 for backslash embedded in multi-line string. (Issue #68)
  • Fix E225 for Python 3 iterable unpacking (PEP 3132). (Issue #72)
  • Enable the new checkers from the E12 series in the default configuration.
  • Suggest less error-prone alternatives for E712 errors.
  • Rewrite checkers to run faster (E22, E251, E27).
  • Fixed a crash when parsed code is invalid (too many closing brackets).
  • Fix E127 and E128 for continuation line indentation. (Issue #74)
  • New option --format to customize the error format. (Issue #23)
  • New option --diff to check only modified code. The unified diff is read from STDIN. Example: hg diff | pep8 --diff (Issue #39)
  • Correctly report the count of failures and set the exit code to 1 when the --doctest or the --testsuite fails.
  • Correctly detect the encoding in Python 3. (Issue #69)
  • Drop support for Python 2.3, 2.4 and 3.0. (Issue #78)

1.2 (2012-06-01)

  • Add E121 through E128 for continuation line indentation. These checks are disabled by default. If you want to force all checks, use switch --select=E,W. Patch by Sam Vilain. (Issue #64)
  • Add E721 for direct type comparisons. (Issue #47)
  • Add E711 and E712 for comparisons to singletons. (Issue #46)
  • Fix spurious E225 and E701 for function annotations. (Issue #29)
  • Add E502 for explicit line join between brackets.
  • Fix E901 when printing source with --show-source.
  • Report all errors for each checker, instead of reporting only the first occurrence for each line.
  • Option --show-pep8 implies --first.

1.1 (2012-05-24)

  • Add E901 for syntax errors. (Issues #63 and #30)
  • Add E271, E272, E273 and E274 for extraneous whitespace around keywords. (Issue #57)
  • Add tox.ini configuration file for tests. (Issue #61)
  • Add .travis.yml configuration file for continuous integration. (Issue #62)

1.0.1 (2012-04-06)

  • Fix inconsistent version numbers.

1.0 (2012-04-04)

  • Fix W602 raise to handle multi-char names. (Issue #53)

0.7.0 (2012-03-26)

  • Now --first prints only the first occurrence of each error. The --repeat flag becomes obsolete because it is the default behaviour. (Issue #6)
  • Allow to specify --max-line-length. (Issue #36)
  • Make the shebang more flexible. (Issue #26)
  • Add testsuite to the bundle. (Issue #25)
  • Fixes for Jython. (Issue #49)
  • Add PyPI classifiers. (Issue #43)
  • Fix the --exclude option. (Issue #48)
  • Fix W602, accept raise with 3 arguments. (Issue #34)
  • Correctly select all tests if DEFAULT_IGNORE == ''.

0.6.1 (2010-10-03)

  • Fix inconsistent version numbers. (Issue #21)

0.6.0 (2010-09-19)

  • Test suite reorganized and enhanced in order to check more failures with fewer test files. Read the run_tests docstring for details about the syntax.
  • Fix E225: accept print >>sys.stderr, "..." syntax.
  • Fix E501 for lines containing multibyte encoded characters. (Issue #7)
  • Fix E221, E222, E223, E224 not detected in some cases. (Issue #16)
  • Fix E211 to reject v = dic['a'] ['b']. (Issue #17)
  • Exit code is always 1 if any error or warning is found. (Issue #10)
  • --ignore checks are now really ignored, especially in conjunction with --count. (Issue #8)
  • Blank lines with spaces yield W293 instead of W291: some developers want to ignore this warning and indent the blank lines to paste their code easily in the Python interpreter.
  • Fix E301: do not require a blank line before an indented block. (Issue #14)
  • Fix E203 to accept NumPy slice notation a[0, :]. (Issue #13)
  • Performance improvements.
  • Fix decoding and checking non-UTF8 files in Python 3.
  • Fix E225: reject True+False when running on Python 3.
  • Fix an exception when the line starts with an operator.
  • Allow a new line before closing ), } or ]. (Issue #5)

0.5.0 (2010-02-17)

  • Changed the --count switch to print to sys.stderr and set exit code to 1 if any error or warning is found.
  • E241 and E242 are removed from the standard checks. If you want to include these checks, use switch --select=E,W. (Issue #4)
  • Blank line is not mandatory before the first class method or nested function definition, even if there’s a docstring. (Issue #1)
  • Add the switch --version.
  • Fix decoding errors with Python 3. (Issue #13 [1])
  • Add --select option which is mirror of --ignore.
  • Add checks E261 and E262 for spaces before inline comments.
  • New check W604 warns about deprecated usage of backticks.
  • New check W603 warns about the deprecated operator <>.
  • Performance improvement, due to rewriting of E225.
  • E225 now accepts:
    • no whitespace after unary operator or similar. (Issue #9 [1])
    • lambda function with argument unpacking or keyword defaults.
  • Reserve “2 blank lines” for module-level logical blocks. (E303)
  • Allow multi-line comments. (E302, issue #10 [1])

0.4.2 (2009-10-22)

  • Decorators on classes and class methods are OK now.

0.4 (2009-10-20)

  • Support for all versions of Python from 2.3 to 3.1.
  • New and greatly expanded self tests.
  • Added --count option to print the total number of errors and warnings.
  • Further improvements to the handling of comments and blank lines. (Issue #1 [1] and others changes.)
  • Check all py files in directory when passed a directory (Issue #2 [1]). This also prevents an exception when traversing directories with non *.py files.
  • E231 should allow commas to be followed by ). (Issue #3 [1])
  • Spaces are no longer required around the equals sign for keyword arguments or default parameter values.
[1](1, 2, 3, 4, 5, 6) These issues refer to the previous issue tracker.

0.3.1 (2009-09-14)

  • Fixes for comments: do not count them when checking for blank lines between items.
  • Added setup.py for pypi upload and easy_installability.

0.2 (2007-10-16)

  • Loads of fixes and improvements.

0.1 (2006-10-01)

  • First release.