append 方法如何在 python 中工作? [英] How does append method work in python?

问题描述

我学习编程语言，有一个测验问题和解决方案是这样的:

I study programming languages and a quiz question and solution was this:

def foo(x):
   x.append (3)
   x = [8]
   return x

x=[1, 5]
y= foo(x)
print x
print y

为什么会这样打印:

[1 5 3 ]
[8]

为什么 x 不等于 8 ??

Why doesn't x equal to 8 ??

推荐答案

另外两个答案很好.我建议您尝试使用 id 来获取地址.

The other two answers are great. I suggest you to try id to get address.

看下面的例子

def foo(x):
   x.append (3)
   print "global",id(x)
   x = [8]
   print "local ",id(x)
   return x

x=[1, 5]
print "global",id(x)
y= foo(x)
print "global",id(x)
print x
print y

和输出

global 140646798391920
global 140646798391920
local  140646798392928
global 140646798391920
[1, 5, 3]
[8]

如您所见，变量 x 的地址在您操作它时保持不变，但在您使用 = 时会发生变化.函数内部的变量赋值使变量局部于函数

As you can see, the address of the variable x remains same when you manipulate it but changes when you use =. Variable assignment inside a function makes the variable local to the function

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