python – 为什么同一语句打印两个不同的值？

发布时间：2020-12-20 12:07:19 所属栏目：Python 来源：网络整理

导读：当我想要理解 python自我概念时,我遇到了这个我认为有用的例子.但是有一部分让我感到困惑.为什么打印a.i输出两个不同的值？在第一种情况下,输出为5,这对我来说很有意义.但后来几行同样打印a.i语句输出123. def say_hi(): return 'hi!'i = 789class MyClass(o

当我想要理解 python自我概念时,我遇到了这个我认为有用的例子.但是有一部分让我感到困惑.为什么打印a.i输出两个不同的值？在第一种情况下,输出为5,这对我来说很有意义.但后来几行同样打印a.i语句输出123.

def say_hi():
    return 'hi!'

i = 789

class MyClass(object):

    i = 5

    def prepare(self):
        i = 10
        self.i = 123
        print i

    def say_hi(self):
        return 'Hi there!'

    def say_something(self):
        print say_hi()

    def say_something_else(self):
        print self.say_hi()

产量

>>> print say_hi()
hi!
>>> print i
789
>>> a = MyClass()
>>> a.say_something()
hi!
>>> a.say_something_else()
Hi there!
>>> print a.i
5
>>> a.prepare()
10
>>> print i
789
>>> print a.i
123

解决方法

您正在使用具有相同名称的全局,本地和实例属性：

def say_hi():        # This is the global function 'say_hi'
    return 'hi!'    

i = 789              # This is the global 'i'

class MyClass(object):

    i = 5  # This is a class attribute 'i'

    def prepare(self):
        i = 10           # Here,you are creating a new 'i' (local to this function)
        self.i = 123     # Here,you are changing the instance attribute 'i'
        print i          # Here,you are printing the new'ed 'i' (now with value 10)

    def say_hi(self):         # This is the object method 'say_hi' function
        return 'Hi there!'

    def say_something(self):
        print say_hi()         # Here,you are calling the global 'say_hi' function

    def say_something_else(self):
        print self.say_hi()    # Here,you are calling the object method 'say_hi' function

所以输出是正确的：

>>> print say_hi()          # global
hi!
>>> print i                 # global
789
>>> a = MyClass()
>>> a.say_something()       # say_something calls the global version
hi!
>>> a.say_something_else()  # say_something_else calls the object version
Hi there!
>>> print a.i               # class attribute 'i'
5
>>> a.prepare()             # prints the local 'i' and change the class attribute 'i'
10
>>> print i                 # global 'i' is not changed at all
789
>>> print a.i               # class attribute 'i' changed to 123 by a.prepare()
123

（编辑：李大同）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!