Question

I want to have each instance of some class have a unique integer identifier based on the order that I create them, starting with (say) 0. In Java, I could do this with a static class variable. I know I can emulate the same sort of behavior with Python, but what would be the most ‘Pythonic’ way to do this?

Thanks

Answer 1

The following approach would be relatively pythonic (for my subjective judgement of pythonic – explicit, yet concise):

class CounterExample(object):

    instances_created = 0

    def __init__(self):
        CounterExample.instances_created += 1

    def __del__(self):
        """ If you want to track the current number of instances
            you can add a hook in __del__. Otherwise use
            __init__ and just count up.
        """
        CounterExample.instances_created -= 1

If you are facing a large number of classes, which need that kind of attribute, you could also consider writing a metaclass for that.

An example of a metaclass: http://www.youtube.com/watch?v=E_kZDvwofHY#t=0h56m10s.