Question :
Python recognizes the following as instruction which defines file’s encoding:
# -*- coding: utf-8 -*-
I definitely saw this kind of instructions before (-*- var: value -*-). Where does it come from? What is the full specification, e.g. can the value include spaces, special symbols, newlines, even -*- itself?
My program will be writing plain text files and I’d like to include some metadata in them using this format.
Answer #1:
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.
Answer #2:
# -*- 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.
Answer #3:
This is so called file local variables, that are understood by Emacs and set correspondingly. See corresponding section in Emacs manual – you can define them either in header or in footer of file
Answer #4:
In PyCharm, I’d leave it out. It turns off the UTF-8 indicator at the bottom with a warning that the encoding is hard-coded. Don’t think you need the PyCharm comment mentioned above.
