Python Common Style Guidelines

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One of the best practices is, to define a common style guideline. So that it would be much easier to understand a codebase when all the code in it, is in a consistent style. Specially if you are working in a team. PEP (Python Enhancement Proposals) provides a good starting point to define those style guide.

Here are some highlights which are mostly from PEP 8, but also from other best practices:

Naming Conventions

Avoid one letter variables like x and y (Except in very short code blocks). Give your variables and functions a meaningful name and use follow naming convention:

  • Variables, functions, packages and modules names should be:

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    lower_case_with_underscores

  • Classes and Exceptions

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    CamelCase

  • Protected methods

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    _single_leading_underscore

  • Private methods

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    __double_leading_underscore

  • Constants

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    ALL_CAPS_WITH_UNDERSCORES

Programming Recommendations

  • Comparisons to singletons like None should always be done with is or is not, never the equality operators.

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    if user is None:  # Use that

    if user == None   # Don't use that

  • For sequences, (strings, lists, tuples), use the fact that empty sequences are false. Don’t use the len() function.

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    if not seq:           # Use that
    if seq:               # Use that

    if len(seq):          # Don't use that
    if not len(seq):      # Don't use that

  • Don’t compare boolean values to True or False using ==

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    if greeting:          # Use that
    if greeting == True:  # Don't use that

Indentation

Use spaces, instead of tabs (your IDE can probably convert tabs automatically to spaces). Taking 2 or 4 spaces are both fine. Just agree a convention in your team. Never mix the indentations.

Imports

Put all imports at the top of the file with three sections, each separated by a blank line, in this order:

  • System imports
  • Third-party imports
  • Local source tree imports

That makes it clear where each module is coming from. Also Imports itself should usually be on separate lines.

Pylint

Pylint is a Python static code analysis tool which looks for programming errors and help to enforce the rules of PEP 8. Most of the IDE’s have an integration of pylint. Personally I use the TensorFlow code style guide, which is based on PEP 8 and Google Python Style Guide. Just download the pylintrc file, which contains all the rules, from e.g. TensorFlow and point your pylint to that file.