member or class variables in python

Question

I come from Java, so I'm getting confused here.

class Sample(object):
    x = 100                     # class var?
    def __init__(self, value):
        self.y = value          # instance var?
        z = 300                 # private var? how do we access this outside Sample?

What is the difference between the 3 variable declarations?

Answer 1

class Sample(object):
    x = 100      
    _a = 1
    __b = 11               
    def __init__(self, value):
        self.y = value      
        self._c = 'private'    
        self.__d = 'more private'
        z = 300         

In this example:

• x is class variable,
• _a is private class variable (by naming convention),
• __b is private class variable (mangled by interpreter),
• y is instance variable,
• _c is private instance variable (by naming convention),
• __d is private instance variable (mangled by interpreter),
• z is local variable within scope of __init__ method.

In case of single underscore in names, it's strictly a convention. It is still possible to access these variables. In case of double underscore names, they are mangled. It's still possible to circumvent that.