python __new__和__init__

• __new__方法实际上在__init__方法之前执行, 用于创建类的实例; __init__方法负责在实例创建后对其进行自定义.

• __new__方法会返回一个创建的实例,而init什么都不返回.

参数在调用类构造函数时首先被传递给new方法, 然后再传递给init方法.

class Person(object):
    def __init__(self, name):
        print "__init__ called"
        self.name = name
person = Person("mike")

输出为:

__init__ called

上述过程实际执行的顺序如下:

class Person(object):
    def __new__(cls, name):
        print "__new__ called first"
        return super(Person, cls).__new__(cls, name)

    def __init__(self, name):
        print "__init__ called"
        self.name = name
person = Person('mike')

输出为:

__new__ called first
__init__ called