Where does this come from: -*- coding: utf-8 -*-
This way of specifying the encoding of a Python file comes from PEP 0263 - Defining Python Source Code Encodings.
It is also recognized by GNU Emacs (see Python Language Reference, 2.1.4 Encoding declarations), though I don't know if it was the first program to use that syntax.
# -*- coding: utf-8 -*- is a Python 2 thing. In Python 3+, the default encoding of source files is already UTF-8 and that line is useless.
See: Should I use encoding declaration in Python 3?
pyupgrade is a tool you can run on your code to remove those comments and other no-longer-useful leftovers from Python 2, like having all your classes inherit from object.