Docstring would prevent it from rambling, but you'd then be required to write the signature first. PEP 257 prescribes the imperative mood: The docstring is a

Docstring would prevent it from rambling, but you'd then be required to write the signature first. PEP 257 prescribes the imperative mood: The docstring is a phrase ending in a period. It prescribes the function or method’s effect as a command (“Do this”, “Return that”), not as a description; e.g. don’t write “Returns the pathname …”.