2.2. The Interpreter and Its Environment
2.2.1. Source Code Encoding
By default, Python source files are treated as encoded in UTF-8.
In that encoding, characters of most languages in the world can be used simultaneously in string literals, identifiers and comments — although the standard library only uses ASCII characters for identifiers, a convention that any portable code should follow.
PEP 0263 — Defining Python Source Code Encodings
Python will default to ASCII as standard encoding if no other encoding hints are given.
The default encoding was set to “ascii” in version 2.5.