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Utility Functions

|Flake8| has a few utility functions that it uses internally.

Warning

As should be implied by where these are documented, these are all internal utility functions. Their signatures and return types may change between releases without notice.

Bugs reported about these internal functions will be closed immediately.

If functions are needed by plugin developers, they may be requested in the bug tracker and after careful consideration they may be added to the documented stable API.

.. autofunction:: flake8.utils.parse_comma_separated_list

:func:`~flake8.utils.parse_comma_separated_list` takes either a string like

"E121,W123,F904"
"E121,\nW123,\nF804"
"E121,\n\tW123,\n\tF804"

Or it will take a list of strings (potentially with whitespace) such as

["   E121\n", "\t\nW123   ", "\n\tF904\n    "]

And converts it to a list that looks as follows

["E121", "W123", "F904"]

This function helps normalize any kind of comma-separated input you or |Flake8| might receive. This is most helpful when taking advantage of |Flake8|'s additional parameters to :class:`~flake8.options.manager.Option`.

.. autofunction:: flake8.utils.normalize_path

This utility takes a string that represents a path and returns the absolute path if the string has a / in it. It also removes trailing /s.

.. autofunction:: flake8.utils.normalize_paths

This function utilizes :func:`~flake8.utils.parse_comma_separated_list` and :func:`~flake8.utils.normalize_path` to normalize its input to a list of strings that should be paths.

.. autofunction:: flake8.utils.stdin_get_value

This function retrieves and caches the value provided on sys.stdin. This allows plugins to use this to retrieve stdin if necessary.

.. autofunction:: flake8.utils.is_windows

This provides a convenient and explicitly named function that checks if we are currently running on a Windows (or nt) operating system.

.. autofunction:: flake8.utils.can_run_multiprocessing_on_windows

This provides a separate and distinct check from :func:`~flake8.utils.is_windows` that allows us to check if the version of Python we're using can actually use multiprocessing on Windows.

.. autofunction:: flake8.utils.is_using_stdin

Another helpful function that is named only to be explicit given it is a very trivial check, this checks if the user specified - in their arguments to |Flake8| to indicate we should read from stdin.

.. autofunction:: flake8.utils.filenames_from

When provided an argument to |Flake8|, we need to be able to traverse directories in a convenient manner. For example, if someone runs

$ flake8 flake8/

Then they want us to check all of the files in the directory flake8/. This function will handle that while also handling the case where they specify a file like:

$ flake8 flake8/__init__.py
.. autofunction:: flake8.utils.fnmatch

The standard library's :func:`fnmatch.fnmatch` is excellent at deciding if a filename matches a single pattern. In our use case, however, we typically have a list of patterns and want to know if the filename matches any of them. This function abstracts that logic away with a little extra logic.

.. autofunction:: flake8.utils.parameters_for

|Flake8| analyzes the parameters to plugins to determine what input they are expecting. Plugins may expect one of the following:

  • physical_line to receive the line as it appears in the file
  • logical_line to receive the logical line (not as it appears in the file)
  • tree to receive the abstract syntax tree (AST) for the file

We also analyze the rest of the parameters to provide more detail to the plugin. This function will return the parameters in a consistent way across versions of Python and will handle both classes and functions that are used as plugins. Further, if the plugin is a class, it will strip the self argument so we can check the parameters of the plugin consistently.

.. autofunction:: flake8.utils.parse_unified_diff

To handle usage of :option:`flake8 --diff`, |Flake8| needs to be able to parse the name of the files in the diff as well as the ranges indicated the sections that have been changed. This function either accepts the diff as an argument or reads the diff from standard-in. It then returns a dictionary with filenames as the keys and sets of line numbers as the value.