class Person:
def __init__(self, ......
def make_friend(self, friend: 'Person') -> None:
.....
I'm learning python and I don't understand this example. Why type condition for friend should be in single quotes? Why not friend: Person? How it can works? Does it have something common with type class shortcut?
The function make_friend is defined before the class Person.
When classes are made, first the namespace (internal class functions) is created, and then it is built into the class (using the __prepare__ method).
Trying to reference Person before it is created will fail.
Solving it can be done with a "forward reference", which can be used with quotes or with a from __future__ import annotations at the top of the file.