In Python, * and ** allow you to capture arguments coming into a callable, even if you don't know their names ahead of time.



In [2]:

    
def foo(*args):
    print repr(args)

foo(1, 2, 3, 4)









    



(1, 2, 3, 4)



In [3]:

    
def bar(**kwargs):
    print kwargs

bar(a=1, b=2, c=3)









    



{'a': 1, 'c': 3, 'b': 2}

This is particularly useful for inheritance, where you may want to override a method of the parent while maintaining the parent's method's functionality. You can do so without even knowing the parent class's signature - and if that signature changes, your descendant class will not break!



In [7]:

    
class Baz(object):
    def my_method(self, a, b):
        print 'a: %s; b: %s' % (a, b)

class Bazlet(Baz):
    def my_method(self, x, *args, **kwargs):
        print 'x: %s' % x
        # Call the parent's corresponding method
        super(Bazlet, self).my_method(*args, **kwargs)

baz = Bazlet()
baz.my_method(x=10, a=1, b=2)









    



x: 10
a: 1; b: 2

Whenever you wrap a method to provide a particular interface, or create a subclass and extend a particular method, using this convention will make your code less fragile.