How do variable scopes work within Python classes?

Variable Scopes in Python Classes

Scope Variation

In Python classes, variable scope varies based on where they're declared:

• Class-level variables (outside functions): Accessible to all class functions (public variables).
• Function-local variables (inside class functions): Restricted to that specific function (within its scope).

self vs. Global Variables

Declaring a variable with self.(variable name) within a class function also makes it accessible to all class functions. However, unlike global variables, these variables are specific to the current instance and do not override class-level variables.

Additional Nuances

• Single vs. Double Underscore Prefix: Variables beginning with a single underscore (e.g., _variable) are considered protected and should only be accessed within the class. Variables beginning with double underscores (e.g., __variable) are mangled and effectively private.
• Local Variables: Variables declared within class functions are local to those functions and don't affect the class scope.

Example

Consider the following class:

class Test:
    a = None
    b = None

    def __init__(self, a):
        print(self.a)
        self.a = a
        self._x = 123
        self.__y = 123
        b = 'meow'

• a and b are class-level variables accessible from any instance.
• a is overridden by the instance-specific self.a in __init__.
• _x is protected and not part of the public API.
• __y is mangled and private to the class.
• b is a local variable accessible only within __init__.

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