class Singleton(object[,...]):

    staticVar1 = None
    staticVar2 = None

    def __init__(self):
        if self.__class__.staticVar1==None :
            # create class instance variable for instantiation of class
            # assign class instance variable values to class static variables
        else:
            # assign class static variable values to class instance variables

在Python中实现单例的一个稍微不同的方法是Alex Martelli(谷歌员工和Python天才)的borg模式。

class Borg:
    __shared_state = {}
    def __init__(self):
        self.__dict__ = self.__shared_state

因此，它们共享状态，而不是强制所有实例具有相同的标识。

由ActiveState提供的Python实现的单例模式。

看起来窍门是把应该只有一个实例的类放在另一个类中。

我的简单解决方案是基于函数参数的默认值。

def getSystemContext(contextObjList=[]):
    if len( contextObjList ) == 0:
        contextObjList.append( Context() )
        pass
    return contextObjList[0]

class Context(object):
    # Anything you want here

请看来自PEP318的实现，使用装饰器实现单例模式:

def singleton(cls):
    instances = {}
    def getinstance():
        if cls not in instances:
            instances[cls] = cls()
        return instances[cls]
    return getinstance

@singleton
class MyClass:
    ...

这是我自己对单例对象的实现。你所要做的就是布置课堂;为了获得单例，你必须使用Instance方法。这里有一个例子:

@Singleton
class Foo:
   def __init__(self):
       print 'Foo created'

f = Foo() # Error, this isn't how you get the instance of a singleton

f = Foo.instance() # Good. Being explicit is in line with the Python Zen
g = Foo.instance() # Returns already created instance

print f is g # True

下面是代码:

class Singleton:
    """
    A non-thread-safe helper class to ease implementing singletons.
    This should be used as a decorator -- not a metaclass -- to the
    class that should be a singleton.

    The decorated class can define one `__init__` function that
    takes only the `self` argument. Also, the decorated class cannot be
    inherited from. Other than that, there are no restrictions that apply
    to the decorated class.

    To get the singleton instance, use the `instance` method. Trying
    to use `__call__` will result in a `TypeError` being raised.

    """

    def __init__(self, decorated):
        self._decorated = decorated

    def instance(self):
        """
        Returns the singleton instance. Upon its first call, it creates a
        new instance of the decorated class and calls its `__init__` method.
        On all subsequent calls, the already created instance is returned.

        """
        try:
            return self._instance
        except AttributeError:
            self._instance = self._decorated()
            return self._instance

    def __call__(self):
        raise TypeError('Singletons must be accessed through `instance()`.')

    def __instancecheck__(self, inst):
        return isinstance(inst, self._decorated)