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Demo on how to define Singleton Classes on Python
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#! /usr/bin/python | |
class Singleton(type): | |
_instances = {} | |
def __call__(cls, *args, **kwargs): | |
if cls not in cls._instances: | |
cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs) | |
return cls._instances[cls] | |
class ExampleClass(object): | |
__metaclass__ = Singleton | |
def __init__(self): | |
self.name = 'World' | |
def set_name(self, name): | |
self.name = name | |
def say_hello(self): | |
print 'Hello, {0}!'.format(self.name) | |
if __name__ == '__main__': | |
print '{0:=^40}'.format(' Create Both Objects ') | |
obj1 = ExampleClass() | |
obj2 = ExampleClass() | |
print '{0:~^40}'.format(' Say Hello before setting any name. ') | |
obj1.say_hello() | |
obj2.say_hello() | |
print '{0:~^40}'.format(' Set Name on Obj 1 to "Earth" ') | |
obj1.set_name('Earth') | |
print '{0:~^40}'.format(' Say Hello only on Obj 2 ') | |
obj2.say_hello() | |
print '{0:~^40}'.format(' Set Name on Obj 2 to "Moon"') | |
obj2.set_name('Moon') | |
print '{0:~^40}'.format(' Say Hello only on Obj 1 ') | |
obj1.say_hello() |
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