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#!/usr/bin/env python

# -*- coding: utf-8 -*-

class Singleton(object):

"""

Assume that only one instance should be created of this class and

it is counting the users connected to the system.

"""

_instance = None

def __new__(cls, *args, **kwargs):

"""

For each class, creating only one instance.

If an instance has been created before, returns the created one.

"""

if not cls._instance:

cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)

# your init codes here

cls.user_count = 0

# end of your init code

return cls._instance

def connect(self):

self.user_count += 1

def disconnect(self):

self.user_count -= 1

if __name__ == '__main__':

s1 = Singleton()

s2 = Singleton()

if id(s1) == id(s2):

print "Same instances"

else:

print "Different instances"

s1.connect() # user count: 1

s1.connect() # user count: 2

s2.connect() # same instance with s1, so user count: 3 for s1 and s2

s1.disconnect() # same instance with s2, so user count: 2 for s1 and s2

print s1.user_count

print s2.user_count