What is a basic example of single inheritance using the super() keyword in Python?

Question

Let's say I have the following classes set up:

class Foo:
     def __init__(self, frob, frotz):
          self.frobnicate = frob
          self.frotz = frotz
class Bar:
     def __init__(self, frob, frizzle):
          self.frobnicate = frob
          self.frotz = 34
          self.frazzle = frizzle

How can I (if I can at all) use super() in this context to eliminate the duplicate code?

Solution 1

In Python >=3.0, like this:

class Foo():
    def __init__(self, frob, frotz)
        self.frobnicate = frob
        self.frotz = frotz

class Bar(Foo):
    def __init__(self, frob, frizzle)
        super().__init__(frob, 34)
        self.frazzle = frizzle

Read more here: http://docs.python.org/3.1/library/functions.html#super

EDIT: As said in another answer, sometimes just using Foo.__init__(self, frob, 34) can be the better solution. (For instance, when working with certain forms of multiple inheritance.)

Solution 2

Assuming you want class Bar to set the value 34 within its constructor, this would work:

class Foo(object):
     def __init__(self, frob, frotz):
          self.frobnicate = frob
          self.frotz = frotz

class Bar(Foo):
     def __init__(self, frob, frizzle):
          super(Bar, self).__init__(frob, frizzle)
          self.frotz = 34
          self.frazzle = frizzle


bar = Bar(1,2)
print "frobnicate:", bar.frobnicate
print "frotz:", bar.frotz
print "frazzle:", bar.frazzle

However, super introduces its own complications. See e.g. super considered harmful. For completeness, here's the equivalent version without super.

class Foo(object):
     def __init__(self, frob, frotz):
          self.frobnicate = frob
          self.frotz = frotz

class Bar(Foo):
     def __init__(self, frob, frizzle):
          Foo.__init__(self, frob, frizzle)
          self.frotz = 34
          self.frazzle = frizzle


bar = Bar(1,2)
print "frobnicate:", bar.frobnicate
print "frotz:", bar.frotz
print "frazzle:", bar.frazzle