Python使用metaclass实现Singleton模式的方法

本文实例讲述了Python使用metaclass实现Singleton模式的方法。分享给大家供大家参考。具体实现方法如下：

class Singleton(type):
  def __call__(cls,*args,**kwargs):
    print "Singleton call"
    if not hasattr(cls,'instance'):
      cls.instance = super(Singleton,cls).__call__(*args,**kwargs)
    return cls.instance
  def __new__(cls,name,bases,dct):
    print "Singleton new"
    return type.__new__(cls,dct)
  def __init__(cls,dct):
    print "Singleton init"
    super(Singleton,cls).__init__(name,dct)
class Cache(object):
  __metaclass__ = Singleton
  def __new__(cls,**kwargs):
    print "Cache new"
    return object.__new__(cls,**kwargs)
  def __init__(cls,**kwargs):
    print "Cache init"
  def __call__(cls,**kwargs):
    print "Cache call"
print Cache()
print Cache()

输出：

Singleton new
Singleton init
Singleton call
Cache new
Cache init
<__main__.Cache object at 0x01CDB130>
Singleton call
<__main__.Cache object at 0x01CDB130>

希望本文所述对大家的Python程序设计有所帮助。