Python Class - How do I create a class that accepts undefined number of arguments?

Question

Im a beginner. For the sake of learning, I have to write a class in python which accepts at most 3 different arguments (a,b,c): something like

 class random(object):

     def __init__(self,a,b,c):
          blah blah blah

How do I make it so that:

• if no argument is entered, it does one thing.

  for example:

  "test=random()", in this case assume a=b=c=0

• if one argument is entered, it does another thing.

  for example:

   "test=random(2)", in this case a=2 ,b=c=0, and then run some case specific codes/instrutctions 

• and etc

something like how with the builtin function/class "range", where you can use

range(9) range(3,9) range(3,9,2)

if you know what I mean.

thanks

Answer 1

It looks like you're asking about Default Argument Values .

When defining a function or method, one way to make parameters optional is to give them default values:

 def __init__(self, a=0, b=0, c=0):

Now, if I call your function (or, in the case of an __init__ function, construct an instance of your class) with no arguments, a , b , and c will all be 0. If I pass 1 argument, b and c will be 0. And so on.

See Arbitrary Argument Lists for another way to do something similar.

---

The way range works is a little funky, because the first argument has a different meaning if there's only 1 argument vs. 2 or more. There are a handful of other builtins like this, but it's not a good idea for you to emulate them; these are basically only there for backward compatibility reasons (to the days when Python didn't have keywords).

To make things more fun, because 0 is a perfectly valid value for start or stop , and so is even None , you have to construct some special value that nobody could reasonably pass you. (That part, you may actually need to emulate some day.) So, it looks something like this:

class range(object):
    _sentinel = object()
    def __init__(self, start_or_stop, stop=range._sentinel, step=None):
        if stop is range._sentinel:
            start, stop = None, start_or_stop
        else:
            start = start_or_stop
        # Now you can use start, stop, step