元類方法__call__ 可以這樣使用：
class TestCall:
def __init__(self, value):
self.value = value
def __call__(self, value = None):
if value is None:
print("value is: ", self.value)
else:
self.value = value
如下：
>>> test = TestCall(7.7)
>>> test.value
7.7
>>> test()
value is: 7.7
>>> test(20200707)
>>> test.value
20200707
>>> test()
value is: 20200707
>>>
調(diào)用__call__實(shí)現(xiàn)python 單例模式
class SingleInstance(type):
instance = None
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def __call__(self, *args, **kwargs):
if self.instance is None:
self.instance = super().__call__(*args, **kwargs)
return self.instance
else:
return self.instance
元類繼承：
class TestSingleInstance(metaclass = SingleInstance):
def __init__(self):
print("Testing start...")
測(cè)試：
>>> my_instance = TestSingleInstance()
Testing start...
>>> my_instance2 = TestSingleInstance()
>>> my_instance is my_instance2
True
>>> my_instance3 = TestSingleInstance()
>>> my_instance3 is my_instance
True
>>>
