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.. currentmodule:: pycodestyle

Developer's notes

Source code

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


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

  • pycodestyle 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 - pycodestyle doesn't want or need a plugin architecture.
  • pycodestyle aims to have no external dependencies.


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 :class:`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 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 --testsuite testsuite
$ python --doctest
$ python --verbose

When contributing to pycodestyle, please observe our Code of Conduct.

To run the tests, the core developer team and Travis CI use tox:

$ pip install -r dev-requirements.txt
$ tox

All the tests should pass for all available interpreters, with the summary of:

congratulations :)


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