What is a clean, Pythonic way to have multiple constructors in Python?

Question

I can't find a definitive answer for this. As far as I know, you can't have multiple __init__ functions in a Python class. So how do I solve this problem?

Suppose I have a class called Cheese with the number_of_holes property. How can I have two ways of creating cheese objects...

1. One that takes a number of holes like this: parmesan = Cheese(num_holes = 15).
2. And one that takes no arguments and just randomizes the number_of_holes property: gouda = Cheese().

I can think of only one way to do this, but this seems clunky:

class Cheese():     def __init__(self, num_holes = 0):         if (num_holes == 0):             # Randomize number_of_holes         else:             number_of_holes = num_holes 

What do you say? Is there another way?

Answer 1

Actually None is much better for "magic" values:

class Cheese():     def __init__(self, num_holes = None):         if num_holes is None:             ... 

Now if you want complete freedom of adding more parameters:

class Cheese():     def __init__(self, *args, **kwargs):         #args -- tuple of anonymous arguments         #kwargs -- dictionary of named arguments         self.num_holes = kwargs.get('num_holes',random_holes()) 

To better explain the concept of *args and **kwargs (you can actually change these names):

def f(*args, **kwargs):    print 'args: ', args, ' kwargs: ', kwargs  >>> f('a') args:  ('a',)  kwargs:  {} >>> f(ar='a') args:  ()  kwargs:  {'ar': 'a'} >>> f(1,2,param=3) args:  (1, 2)  kwargs:  {'param': 3} 

http://docs.python.org/reference/expressions.html#calls