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Multiple syntax checker for Python in Emacs, using Flycheck

Copyright Marc Sherry

This package provides a way to run multiple syntax checkers on Python code, in parallel. The list of supported checkers includes:

This is an alternative way of running multiple Python syntax checkers in Flycheck that doesn't depend on Flycheck's chaining mechanism.

Flycheck is opinionated about what checkers should be run, and chaining is difficult to get right (e.g. see flycheck/flycheck#836, flycheck/flycheck#1300). This package assumes that the user knows what they want, and can configure their checkers accordingly -- if they want to run both flake8 and pylint, that's fine.

This also allows us to run multiple syntax checkers in parallel, rather than sequentially.

Quick start

Installation via MELPA is easiest:

M-x package-install <RET> flycheck-pycheckers <RET>

Then, in your init.el:

(global-flycheck-mode 1)
(with-eval-after-load 'flycheck
  (add-hook 'flycheck-mode-hook #'flycheck-pycheckers-setup))

Start editing a Python file!

For more details on using Flycheck in general, please see The error list (viewable with flycheck-list-errors, bound to C-c ! l by default) shows a unified view of all errors found by all checkers, with line and column information where available.


flycheck-pycheckers can run over any Python file right away, without needing to set up virtual environments or driver scripts. You will simply need to ensure that the checkers you want to run (pep8, mypy, flake8, etc.) are installed somewhere on your PATH where Emacs can find them.



  • Other Flycheck-based checkers -- Some are officially part of the Flycheck package, and some (like this one) are external plugins.
  • Flymake -- Flymake is an older syntax-checking minor mode for Emacs, and is generally less supported and featureful than Flycheck.

Configuration options

You can use this package without needing to get into these details at first -- they are intended for power users and those needing more customization.

There are a number of options that can be customized via customize-variable, which all start with flycheck-pycheckers-. These include:

  • flycheck-pycheckers-args - general arguments to pass to
  • flycheck-pycheckers-checkers - the set of checkers to run (pylint, pep8, mypy, etc.). Can be set in .pycheckers files with the variable checkers as a comma-separated list of checker names.
  • flycheck-pycheckers-ignore-codes - a set of error codes to universally ignore. These can be set more granularly (e.g. per-project) using the .pycheckers file described below.
  • flycheck-pycheckers-max-line-length - the default maximum line length. Can be overridden via .pycheckers file.
  • flycheck-pycheckers-multi-thread - whether to run each checker simultaneously in its own thread, for performance.
  • flycheck-pycheckers-venv-root - a directory containing Python virtual environments, so that imports may be found.

Additionally, a .pycheckers file may be created in a directory to control options for every file under this directory. These files may be logically combined, so a project may have one set of options that may be selectively overridden in a specific subdirectory.

Example .pycheckers file:

max_line_length = 120
mypy_config_file = ci/mypy.ini

Variables that can be set in the configuration file include the following. Note that these are implemented as modifying the values received by argparse in the script, so running bin/ --help is a good way to find other options that may be specified.

  • <checker>_command - a customized command for running a given checker. For example, if you work at a company that provides its own driver script/daemon for running mypy, give the path to the daemon here as mypy_command = /usr/local/bin/mypy-daemon.
  • max-line-length - the maximum allowable line-length. This is a good option to place in a project-specific directory if you have a personal line length preference set by default via flycheck-pycheckers-max-line-length, but also work on projects that follow different standards.
  • checkers - a comma-separated list of checkers to be run for files under this directory. If, for instance, pep8 should not be run on a directory of auto-generated code, this option can accomplish that.
  • ignore_codes - a comma-separated list of error/warning codes to ignore for files under this directory. Replaces the current set of codes completely.
  • merge_configs - whether to keep traversing upwards when parsing .pycheckers files, or stop at this one.
  • extra_ignore_codes - a comma-separated list of error/warning codes to add to the current set of ignored errors. This can be used to make certain directories conform to different levels of syntax enforcement. For example, a directory containing auto-generated code may omit various warnings about indentation or code style.
  • pylint_rcfile - the location of a project-specific configuration file for pylint
  • mypy_config_file - the location of a project-specific configuration file for mypy
  • flake8_config_file - the location of a project-specific configuration file for flake8

Converted from flycheck-pycheckers.el by el2markdown.


Multiple syntax checker for Python in Emacs, using Flycheck







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