Singleton in Python

Singleton in Python

   晚上7:04       Rain Lin

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運用Singleton可以讓物件同時間只會產生一份，這樣就可以避免共用資源的race condition發生。



def singleton(cls):
    instances = {}

    def getinstance(*args, **kwds):
        return instances.setdefault(cls, cls(*args, **kwds))

    return getinstance

class Foo(object):
    def __init__(self, attr=1):
        self.attr = attr
        self.counter = 0

    def add_count(self):
        self.counter = self.counter + 1

Foo = singleton( Foo )

if __name__ == "__main__":
    ins1 = Foo(2)
    ins1.add_count()
    print "Foo(2) -> id(ins)=%d, ins.attr=%d,%s" % (id(ins1), ins1.attr, ('error','ok')[ins1.attr==2])
    print "Foo(2) counter: %d" %ins1.counter
    ins2 = Foo(3)
    ins2.add_count()
    print "Foo(3) -> id(ins)=%d, ins.attr=%d,%s" % (id(ins2), ins2.attr, ('error','ok')[ins2.attr==2])
    print "Foo(3) counter: %d" %ins2.counter
    ins2.attr = 5
    print "ins.attr=5 -> ins.attr=%d, %s" %(ins2.attr,('error','ok')[ins2.attr==5])


執行結果:
root@ubuntu:/mnt/test# python singleton.py
Foo(2) -> id(ins)=140287766113104, ins.attr=2,ok
Foo(2) counter: 1
Foo(3) -> id(ins)=140287766113104, ins.attr=2,ok
Foo(3) counter: 2
ins.attr=5 -> ins.attr=5, ok