單例類
單例是一種模式,它將類的例項化限制為一個例項/物件。有關 python singleton 設計模式的更多資訊,請參見此處 。
class Singleton:
def __new__(cls):
try:
it = cls.__it__
except AttributeError:
it = cls.__it__ = object.__new__(cls)
return it
def __repr__(self):
return '<{}>'.format(self.__class__.__name__.upper())
def __eq__(self, other):
return other is self
另一種方法是裝飾你的類。按照此答案的示例建立一個 Singleton 類:
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. 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.
Limitations: The decorated class cannot be inherited from.
"""
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)
要使用,你可以使用 Instance
方法
@Singleton
class Single:
def __init__(self):
self.name=None
self.val=0
def getName(self):
print(self.name)
x=Single.Instance()
y=Single.Instance()
x.name='I\'m single'
x.getName() # outputs I'm single
y.getName() # outputs I'm single