Python Coding Standards#

Rules for coding standards are driven by the need for readability and consistency (which aids readability). While some people are happy to read inconsistent code, other people find inconsistency to be distracting and their needs should be respected.

Python version#

The LFRic project uses only Python version 3. We track version deprecation so as support ends for Python versions we stop supporting them too. At the time of writing the oldest supported version was 3.9.

Style guide#

There exists already a widely used style guide known as PEP 8. All new or modified Python code in LFRic trunk must be PEP8 compliant.

To check whether your code is PEP8 compliant, run the flake8 tool style checker on your source file, i.e:

flake8 /path/to/file.py

Resolve all errors and warnings (but see E402 exception below).

Flake8 is available in the LFRic software stack on SPICE Desktop and servers.

Copyright#

Every Python source file should have the following mast-head:

##############################################################################
# (c) Crown copyright Met Office. All rights reserved.
# The file LICENCE, distributed with this code, contains details of the terms
# under which the code may be used.
##############################################################################

Whitespace#

Unlike Fortran, Python supports the tab character but we should continue to use only spaces for indentation. Spaces don’t change size between editors and platforms.

Labels#

Labels appear as names for variables, classes and functions. In order to match our Fortran style we mandate pothole_case for these labels. However we do not mandate the addition of suffixes like “_type”. These exist in the Fortran standard for technical reasons which do not apply to Python.

E402#

When running plotting scripts in batch mode, it is common to set the backend before importing pyplot:

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

When flake8 is run on this code, the following error is raised:

test.py:3:1: E402 module level import not at top of file

This deviation from PEP8 is considered to be acceptable for plotting scripts which require batch processing only. In these cases please add the # noqa: E402 directive to the matplotlib.pyplot import line.

Parenthesis#

Deprecated since version 2020: We mandated a space between parenthesis and argument lists (as we do for Fortran), however this is not PEP8 compliant (the existing code shall be updated when it is modified).