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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()