Python_中__init__和__new_

1：__new__:它是创建对象时调用，会返回当前对象的一个实例；

__init__:它是创建对象后调用，对当前对象的一些实例初始化，无返回值

代码示例：

>>> class Data(object):

    def __init__(cls):

        cls.x = 2

        print "init"

        return cls    ###在init中不可用

>>> data = Data()

init

Traceback (most recent call last):

  File "<pyshell#100>", line 1, in <module>

    data = Data()

TypeError: __init__() should return None, not 'Data'

>>> class Data(object):

    def __new__(cls):

        cls.x = 3

        print "new"

        return cls

>>> data = Data()

new

>>> data.x

3

由上可见，__new__方法会返回所构造的对象，__init__则不会，__init__无返回值

2：再类中，若__new__和__init__同时存在时，先调用__new__

代码示例：

>>> class Data(object):

    def __new__(self):

        print "new"

    def __init__(self):

        print "init"

>>> data = Data()

new

3：If __new__() returns an instance of cls, then the new instance’s __init__() method will be invoked like __init__(self[, ...]), where self is the new instance and the remaining arguments are the same as were passed to __new__().

如果__new__返回一个对象的实例，会隐式调用__init__

If __new__() does not return an instance of cls, then the new instance’s __init__() method will not be invoked.

如果__new__不返回一个对象的实例，__init__不会被调用

代码示例：

>>> class A(object):

    def __new__(Class):

        object = super(A,Class).__new__(Class)

        print "in new"

        return object   ##返回对象的实例

    def __init__(self):

        print "in init"

>>> A()

in new

in init

<__main__.A object at 0x0215CD70>

>>> class B(object):

    def __new__(cls):

        print "in new"

        return cls

    def __init__(self):

        print "in init"

>>> b=B()

in new

巴特西

Python_中init和new的异同

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巴特西

Python_中__init__和__new__的异同

最新文章

热门文章

Python_中init和new的异同