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Home / Python

Python Coding Conventions

Our rules for Python code in Unreal Engine are fairly straight-forward: Stick to PEP 8 and you're good.

Depending on how much Python code you write and how runtime-critical it is you may want to extend those rules for certain projects, but even then I would discourage coming up with your own rules and instead use the Google Python Style Guide instead. It's more verbose than PEP 8 and contains more guidelines on how to write and document code.

I don't want to copy-paste big parts of either those conventions here and reccommend you pick either one of them and stick with it. Nevertheless, here is a bullet point list of a few rules that are often ignored by newcomers to Python, especially in an Unreal context where they are sometimes at odds with the C++ style guide.

  • Use 4 spaces for indentation (with exceptions for hanging indents / continuation lines)

  • Encode files in UTF-8

  • Refer to this table for naming (copied from the Google Python Style Guide based on Guido's Recommendations)

    Type Public Internal
    Packages lower_with_under
    Modules lower_with_under _lower_with_under
    Classes CapWords _CapWords
    Exceptions CapWords
    Functions lower_with_under() _lower_with_under()
    Global/Class Constants CAPS_WITH_UNDER _CAPS_WITH_UNDER
    Global/Class Variables lower_with_under _lower_with_under
    Instance Variables lower_with_under _lower_with_under (protected)
    Method Names lower_with_under() _lower_with_under() (protected)
    Function/Method Parameters lower_with_under
    Local Variables lower_with_under

    I know, these rules conflict with the typical UE4 naming conventions, but this is Python code after all. UE4 exports types in CapWords and functions as lower_with_under too.

  • File names should stick to the naming rules of Modules suffixed with .py file extension, e.g. my_module.py

  • Use a main function instead of writing script code into the main file scope. This makes files cleaner and makes it possible to import them into other files.

  • Don't forget docs!

  • UE4 specific: Use unreal.log(), etc in favor of Python's native logging functions

  • Use the following sorting for files:

    1. Module Docstring

    2. From future imports

    3. Module level "dunders" (e.g. all, author, etc)

    4. Imports sorted like this:

      1. Standard library imports.
      2. Related third party imports.
      3. Local application/library specific imports.

    5. Classes and functions (no preferred order)

    6. Main function

    7. Module execution code

      Should be an equivalent of the following in most cases:

      if __name__ == '__main__':
    main()