class methods parameters python

1class Foo          (object):
2    # ^class name  #^ inherits from object
3
4    bar = "Bar" #Class attribute.
5
6    def __init__(self):
7        #        #^ The first variable is the class instance in methods.  
8        #        #  This is called "self" by convention, but could be any name you want.
9        #^ double underscore (dunder) methods are usually special.  This one 
10        #  gets called immediately after a new instance is created.
11
12        self.variable = "Foo" #instance attribute.
13        print self.variable, self.bar  #<---self.bar references class attribute
14        self.bar = " Bar is now Baz"   #<---self.bar is now an instance attribute
15        print self.variable, self.bar  
16
17    def method(self, arg1, arg2):
18        #This method has arguments.  You would call it like this:  instance.method(1, 2)
19        print "in method (args):", arg1, arg2
20        print "in method (attributes):", self.variable, self.bar
21
22
23a = Foo() # this calls __init__ (indirectly), output:
24                 # Foo bar
25                 # Foo  Bar is now Baz
26print a.variable # Foo
27a.variable = "bar"
28a.method(1, 2) # output:
29               # in method (args): 1 2
30               # in method (attributes): bar  Bar is now Baz
31Foo.method(a, 1, 2) #<--- Same as a.method(1, 2).  This makes it a little more explicit what the argument "self" actually is.
32
33class Bar(object):
34    def __init__(self, arg):
35        self.arg = arg
36        self.Foo = Foo()
37
38b = Bar(a)
39b.arg.variable = "something"
40print a.variable # something
41print b.Foo.variable # Foo