Once you have learned how to invoke Flake8, you will soon want to learn how to configure it so you do not have to specify the same options every time you use it.
This section will show you how to make
Remember that you want to specify certain options without writing
flake8 --select E123,W456 --enable-extensions H111
Flake8 supports storing its configuration in the following places:
- Your top-level user directory
- In your project in one of
Values set at the command line have highest priority, then those in the project configuration file, then those in your user directory, and finally there are the defaults. However, there are additional command line options which can alter this.
Flake8 allows a user to use “global” configuration file to store preferences. The user configuration file is expected to be stored somewhere in the user’s “home” directory.
- On Windows the “home” directory will be something like
- On Linux and other Unix like systems (including OS X) we will look in
Note that Flake8 looks for
~\.flake8 on Windows and
on Linux and other Unix systems.
User configuration files use the same syntax as Project Configuration files. Keep reading to see that syntax.
Flake8 is written with the understanding that people organize projects into sub-directories. Let’s take for example Flake8’s own project structure
flake8 ├── docs │ ├── build │ └── source │ ├── _static │ ├── _templates │ ├── dev │ ├── internal │ └── user ├── flake8 │ ├── formatting │ ├── main │ ├── options │ └── plugins └── tests ├── fixtures │ └── config_files ├── integration └── unit
In the top-level
flake8 directory (which contains
tests) there’s also
setup.cfg files. In our case,
we keep our Flake8 configuration in
tox.ini. Regardless of whether you
keep your config in
tox.ini we expect you
to use INI to configure Flake8 (since each of these files already uses INI
as a format). This means that any Flake8 configuration you wish to set needs
to be in the
flake8 section, which means it needs to start like so:
Each command-line option that you want to specify in your config file can be named in either of two ways:
- Using underscores (
_) instead of hyphens (
- Simply using hyphens (without the leading hyphens)
Not every Flake8 command-line option can be specified in the configuration file. See our list of options to determine which options will be parsed from the configuration files.
Let’s actually look at Flake8’s own configuration section:
[flake8] ignore = D203 exclude = .git,__pycache__,docs/source/conf.py,old,build,dist max-complexity = 10
This is equivalent to:
flake8 --ignore D203 \ --exclude .git,__pycache__,docs/source/conf.py,old,build,dist \ --max-complexity 10
In our case, if we wanted to, we could also do
[flake8] ignore = D203 exclude = .git, __pycache__, docs/source/conf.py, old, build, dist max-complexity = 10
This allows us to add comments for why we’re excluding items, e.g.
[flake8] ignore = D203 exclude = # No need to traverse our git directory .git, # There's no value in checking cache directories __pycache__, # The conf file is mostly autogenerated, ignore it docs/source/conf.py, # The old directory contains Flake8 2.0 old, # This contains our built documentation build, # This contains builds of flake8 that we don't want to check dist max-complexity = 10
Following the recommended settings for Python’s configparser, Flake8 does not support inline comments for any of the keys. So while this is fine:
[flake8] per-file-ignores = # imported but unused __init__.py: F401
this is not:
[flake8] per-file-ignores = __init__.py: F401 # imported but unused
If you’re using Python 2, you will notice that we download the
configparser backport from PyPI. That backport enables us to
support this behaviour on all supported versions of Python.
Please do not open issues about this dependency to Flake8.
You can also specify
max_complexity = 10.
This is also useful if you have a long list of error codes to ignore. Let’s
look at a portion of a project’s Flake8 configuration in their
[flake8] # it's not a bug that we aren't using all of hacking, ignore: # F812: list comprehension redefines ... # H101: Use TODO(NAME) # H202: assertRaises Exception too broad # H233: Python 3.x incompatible use of print operator # H301: one import per line # H306: imports not in alphabetical order (time, os) # H401: docstring should not start with a space # H403: multi line docstrings should end on a new line # H404: multi line docstring should start without a leading new line # H405: multi line docstring summary not separated with an empty line # H501: Do not use self.__dict__ for string formatting ignore = F812,H101,H202,H233,H301,H306,H401,H403,H404,H405,H501
They use the comments to describe the check but they could also write this as:
[flake8] # it's not a bug that we aren't using all of hacking ignore = # F812: list comprehension redefines ... F812, # H101: Use TODO(NAME) H101, # H202: assertRaises Exception too broad H202, # H233: Python 3.x incompatible use of print operator H233, # H301: one import per line H301, # H306: imports not in alphabetical order (time, os) H306, # H401: docstring should not start with a space H401, # H403: multi line docstrings should end on a new line H403, # H404: multi line docstring should start without a leading new line H404, # H405: multi line docstring summary not separated with an empty line H405, # H501: Do not use self.__dict__ for string formatting H501
Or they could use each comment to describe why they’ve ignored the check. Flake8 knows how to parse these lists and will appropriately handle these situations.
Using Local Plugins¶
New in version 3.5.0.
Flake8 allows users to write plugins that live locally in a project. These
plugins do not need to use setuptools or any of the other overhead associated
with plugins distributed on PyPI. To use these plugins, users must specify
them in their configuration file (i.e.,
tox.ini). This must be configured in a separate INI section named
Users may configure plugins that check source code, i.e.,
plugins, and plugins that report errors, i.e.,
An example configuration might look like:
[flake8:local-plugins] extension = MC1 = project.flake8.checkers:MyChecker1 MC2 = project.flake8.checkers:MyChecker2 report = MR1 = project.flake8.reporters:MyReporter1 MR2 = project.flake8.reporters:MyReporter2
Flake8 will also, however, allow for commas to separate the plugins for example:
[flake8:local-plugins] extension = MC1 = project.flake8.checkers:MyChecker1, MC2 = project.flake8.checkers:MyChecker2 report = MR1 = project.flake8.reporters:MyReporter1, MR2 = project.flake8.reporters:MyReporter2
These configurations will allow you to select your own custom reporter plugin that you’ve designed or will utilize your new check classes.
If your package is installed in the same virtualenv that Flake8 will run
from, and your local plugins are part of that package, you’re all set; Flake8
will be able to import your local plugins. However, if you are working on a
project that isn’t set up as an installable package, or Flake8 doesn’t run
from the same virtualenv your code runs in, you may need to tell Flake8 where
to import your local plugins from. You can do this via the
paths option in
local-plugins section of your config:
[flake8:local-plugins] extension = MC1 = myflake8plugin:MyChecker1 paths = ./path/to
Relative paths will be interpreted relative to the config file. Multiple paths
can be listed (comma separated just like
exclude) as needed. If your local
plugins have any dependencies, it’s up to you to ensure they are installed in
whatever Python environment Flake8 runs in.
These plugins otherwise follow the same guidelines as regular plugins.