为什么';t Python在创建实例时调用实例方法uuu init uuuu(),但调用提供的类uuu init uuuu()?
我正在超越类的为什么';t Python在创建实例时调用实例方法uuu init uuuu(),但调用提供的类uuu init uuuu()?,python,object,methods,instances,Python,Object,Methods,Instances,我正在超越类的\uuuunew\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu。Python似乎调用了提供的类\uuuu init\uuu()方法,而不是特定于实例的方法,尽管 说: 典型的实现通过调用 使用super(currentclass,cls)的超类的uuuu new_uuu()方法 使用适当的参数,然后将新创建的实例修改为 在归还之前需要 如果u
\uuuunew\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu。Python似乎调用了提供的类\uuuu init\uuu()
方法,而不是特定于实例的方法,尽管
说:
典型的实现通过调用
使用super(currentclass,cls)的超类的uuuu new_uuu()方法
使用适当的参数,然后将新创建的实例修改为
在归还之前需要
如果uuuuuuuuuuuuuuuuuuu()返回cls的实例,则新实例的uuuuu init_uuuuuuu()方法
将像uuu init(self[,…])一样调用,其中self是新实例,self是
其余参数与传递给_new__;()的参数相同
以下是我的测试代码:
#!/usr/bin/env python
import new
def myinit(self, *args, **kwargs):
print "myinit called, args = %s, kwargs = %s" % (args, kwargs)
class myclass(object):
def __new__(cls, *args, **kwargs):
ret = object.__new__(cls)
ret.__init__ = new.instancemethod(myinit, ret, cls)
return ret
def __init__(self, *args, **kwargs):
print "myclass.__init__ called, self.__init__ is %s" % self.__init__
self.__init__(*args, **kwargs)
a = myclass()
哪个输出
$ python --version
Python 2.6.6
$ ./mytest.py
myclass.__init__ called, self.__init__ is <bound method myclass.myinit of <__main__.myclass object at 0x7fa72155c790>>
myinit called, args = (), kwargs = {}
$python--版本
Python 2.6.6
$./mytest.py
myclass.\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
调用myinit,args=(),kwargs={}
运行myinit()
的唯一方法似乎是显式地将其称为self。myclass中的
,各种特殊方法(包括\uuu init\uuuuuu
,但也包括\uu add\uuuuu
等运算符重载)都是可用的。不仅如此,它们还不能通过类或元类上的\uuuu getattr\uuuuuuuu
或\uuuuuuu getattribute\uuuuuuuu
方法访问,它们必须直接位于类上。这是为了提高效率:
以这种方式绕过\uuuu getattribute\uuuu()
机器,为解释器内的速度优化提供了很大的空间,但代价是在处理特殊方法时有一定的灵活性(必须在类对象本身上设置特殊方法,以便解释器一致地调用)
现在还不完全清楚您想要完成什么,但您可以在这里做的一件事是在\uuuu new\uuu
方法中对myclass
进行子类化:
class myclass(object):
def __new__(cls, *args, **kwargs):
class subcls(cls):
def __new__(cls, *args, **kwargs):
return object.__new__(cls)
subcls.__init__ = myinit
return subcls(*args, **kwargs)
新样式类上的特殊方法是在实例的类型上查找的,而不是在实例本身上查找的。这是:
对于新样式的类,只有在对象的类型上定义了特殊方法的隐式调用,而不是在对象的实例字典中定义了特殊方法的隐式调用,才能保证其正常工作。这种行为是以下代码引发异常的原因(与旧式类的等效示例不同):
>>C类(对象):
... 通过
...
>>>c=c()
>>>c.。__len__;=λ:5
>>>莱恩(c)
回溯(最近一次呼叫最后一次):
文件“”,第1行,在
TypeError:类型“C”的对象没有len()
为什么Python在创建实例时不调用实例方法init(),而是调用提供的类init()
看看这个例子
class C:
one = 42
def __init__(self,val):
self.two=val
ci=C(50)
print(ci.__dict__)
print(C.__dict__)
结果如下:
{'two': 50}
{'__module__': '__main__', 'one': 42, '__init__': <function C.__init__ at 0x00000213069BF6A8>, '__dict__': <attribute '__dict__' of 'C' objects>, '__weakref__': <attribute '__weakref__' of 'C' objects>, '__doc__': None}
{'two':50}
{“模块”:“主模块”:“一”:42,“初始模块”:“指令模块”:“weakref”:“无”
请注意,只有值{'two':50}
是实例dict的一部分
'one':42
属于一个类C
dict。\uuuu init\uuu
方法也是如此
这是每种设计
{'two': 50}
{'__module__': '__main__', 'one': 42, '__init__': <function C.__init__ at 0x00000213069BF6A8>, '__dict__': <attribute '__dict__' of 'C' objects>, '__weakref__': <attribute '__weakref__' of 'C' objects>, '__doc__': None}