An introduction to Python Type Hints

Type annotations can also be used to annotate class and instance variables in class bodies and methods.

In particular, the value-less notation: a: int allows one to annotate instance variables that should be initialized in __init__ or __new__. See the syntax in the picture.

As one knows, defining class member variables is not mandatory but it’s useful for providing autocomplete functionality while coding.

The differences between class and instance variables are discussed in the following idea

When one defines a member variable in the class body definition, the interpreter considers it a class variable.

class Dog:

name: str = ‘Doggo’ # class variable

In the __init__ constructor, one does have access at the ‘name’ class variable using ‘self’. But as self represents the instance of the class, in the constructor scope, ‘self.name’ becomes an instance variable.

By deleting the ‘name’ attribute from a Dog instance, one can access the ‘name’ class variable once again.