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