====== Checking Python Code Style and Syntax ======

The following steps enable you to check your Python code for syntax errors, coding style and standards ([[http://www.python.org/dev/peps/pep-0008/|PEP 8]])


===== Using pycodestyle and pylint =====

The following steps enable you to check your code with Pylint, Pyflakes and Pycodestyle (formerly known as pep8).


==== Helper script ====

You need a little helper script to combine the above (and maybe other) tools
to be run at once. Save this script somewhere into your $PATH or at some
other location of your choice and make it executable.

<file bash check_python_code>
#!/bin/sh

echo "======  pycodestyle  ======"
pycodestyle $1
echo "======  pyflakes  ======"
pyflakes $1
echo "======  pylint  ======"
pylint --msg-template="{path}:{line}: [{msg_id}({symbol}), {obj}] {msg}" --reports=n $1
pylint -f parseable -r n $1
</file>


You can also set environment variables like PYTHONPATH to extend or reduce the
path for Python to look for modules in this script, e.g. by simply exporting
the variable:

<code bash>
export PYTHONPATH="$PYTHONPATH:/home/username/.pylint.d"
</code>



==== Setup Geany ====

{{ :howtos:images:check_python_code.png?direct&300|}}

  - Open a Python file in Geany or simply create a new file and set the filetype to Python.
  - Open the //Set Build Commands// dialog in the Build menu.
  - Setup the custom command
    * Set a label, e.g. "Check"
    * Set the Command field to <code>
check_python_code %f
</code> Note: this assumes that you saved the above mentioned helper script into a path in your $PATH environment variable. If not, just specify the full path to the script. %f is a placeholder replaced by Geany on execution with the filename of the current file in the editor. OR You can also use each command i.e. `pep8`, `pyflakes` or `pylint` directly in place of `check_python_code` 
  - Paste the following text in the "Error regular expression" field. <code>
([^:]+):([0-9]+):([0-9:]+)? .*
</code> This is used by Geany to parse the output of build commands for errors to be highlighted in the editor.


==== Using pylint on Windows ====

Gösta Ljungdahl mentioned, the following little batch script is useful to use pylint on Windows with Geany:

<code dos pylint.bat>
@echo off
set configfile=c:\cygwin64\home\gostal\.pylintrc
echo "======  pylint  ======"
c:\Anaconda\envs\python3\Scripts\pylint.exe --rcfile=%configfile% --msg-template="{path}:{line}: [{msg_id}({symbol}), {obj}] {msg}" %1
</code>

Of course, you need to tweak the paths to the config file and pylint.exe.
The rest should be similar to the explainations above.



===== Using flake8 =====

[[https://pypi.python.org/pypi/flake8|Flake8]] is a wrapper around several tools (PyFlakes, pep8 and Ned Batchelder's McCabe script), which also allows integration with plugins.

Using it offers a convenient and simple alternative to using the //Helper Script// approach described earlier in this document. 

==== Setup ====

  - Install the necessary tools <code bash>
pip install flake8 pep8-naming
</code>
  - Configure Geany as described in the [[howtos:check_python_code#setup_geany|previous section]], the only difference being the command to execute (use the same regular expression) <code>
flake8 --show-source "%f"</code>


===== Usage in Geany =====

After saving the helper script and setting up Geany's build commands, you are
ready to use this by simply **pressing F9** or using the **menu Build -> Check** to
trigger the execution of the helper script and so let the tools check your
code. 

All errors and warnings reported by the tools are sent to the Compiler tab
in the messages windows at the bottom of the Geany window.
You can see the errors for review, click on them to jump to the corresponding
code line and Geany will also mark the reported code lines directly in the editor
with red squiggly underlines.

Ideally, you won't see much errors in your code :). Good luck.


{{tag>howto python pep8 pycodestyle pyflakes python flake8}}