With flake8 it is possible enforcing a style guide to hand written python code. By default flake8 includes checks provided by PyFlakes, PEP-0008 inspired style checks provided by PyCodeStyle, and McCabe complexity checking.

Installation

aptitude install flake8

Versions

Debian Stretch

flake8 --version
3.2.1 (mccabe: 0.5.3, pyflakes: 1.3.0, pycodestyle: 2.2.0) CPython 3.5.3 on Linux

Debian Buster

flake8 --version
3.6.0 (mccabe: 0.6.1, pycodestyle: 2.4.0, pyflakes: 2.0.0) CPython 3.7.3 on Linux

Debian Bullseye

flake8 --version
3.8.4 (mccabe: 0.6.1, pycodestyle: 2.6.0, pyflakes: 2.2.0) CPython 3.9.2 on Linux

Usage

The command line tool flake8 can be used on a single file or on multiple files.

Single File Usage

python3 flake8 /PATH/TO/file.py

Multiple File Usage

python3 flake8 /PATH/TO/FILES/*.py

Output

The command flake8 prints a list of issues found. While most of them are related to style it also prints if it found a variable assigned but not used. (Perl is doing this automatically via -w option).

Useful Command Line Options

While flake8 is usable already without options, it can be customized via a configuration file or various options. This sections shows only a small subset of useful command line options.

• -q --quite: Just print the name of file in which issues are found
• --config=CONFIG: specify the configuration file (for custom options)
• --max-line-length=n: set different line length (default 79)

Ignoring Errors (Violations)

Ignoring Files Or Directory

To ignore whole files or directories

flake8 --exclude path/to/file

Ignoring Error (Violation) Types

To ignore certain error (violation) types, it is possible to provide the ID on the command line. (It is also possible to it in a configuration file)

New exclude list:

flake8 --ignore=E1,E23,W503 path/to/files/

Extending the exclude list:

flake8 --extend-ignore=E1,E23 path/to/files/

Ignoring Lines

If the line is short enough it is possible to ignore one line with a special comment # noqa.

example = lambda: 'example'  # noqa: E731

Discussion

Having flake8 under Python is nice to have. Compared with other solutions, like perltidy, it seems this tool needs to go a long way before it is as easy to use, useful and time saving. A short example: When using an editor (like vim) it is possible to define a hot key to activate perltidy to format the displayed code. So as a programmer one do not need to write all the indentations and other fancy spaces or alignments. Just hit that key and the code looks beautiful. With flake8 the programmer gets just a report and has to fix all manually. perltidy can batch convert files, check files embedded in other markup (HTML for example) and much more. As Python has in contrast to Perl the syntax philosophy “there is only one way” it is of course no wonder that flake8 do not offer much to customize syntax, but one real advantage of flake8 is, that it print out IDs referencing the rules, that can be used up to look up and find more information about specific rules.

History

Version	Date	Notes
0.1.1	2022-07-06	History, shell->bash, Debian 11 Bullseye
0.1.0	2020-05-08	Initial release