Python入门系列：References

非法入侵

References
当你创建对象并把它赋给一个变量后，这个变量仅仅只是关联到(refer to)这个对象，而并不代表这个对象本身。这就意味着变量名指向了你的计算机的内存中对象保存的位置。这个叫做把变量名绑定到对象上(This is called as binding of the name to the object)。
通常你并不需要太关注这个问题，但却会对你的应用有微妙的影响，所以你需要意识到这个问题。
请看下面的示例：
# Filename: reference.py
print('Simple Assignment')
shoplist = ['apple', 'mango', 'carrot', 'banana']
mylist = shoplist # mylist is just another name pointing to the same
object!
del shoplist[0] # I purchased the first item, so I remove it from the
list
print('shoplist is', shoplist)
print('mylist is', mylist)
# notice that both shoplist and mylist both print the same list without
# the 'apple' confirming that they point to the same object
print('Copy by making a full slice')
mylist = shoplist[:] # make a copy by doing a full slice
del mylist[0] # remove first item
print('shoplist is', shoplist)
print('mylist is', mylist)
# notice that now the two lists are different
输出结果：
$ python reference.py
Simple Assignment
shoplist is ['mango', 'carrot', 'banana']
mylist is ['mango', 'carrot', 'banana']
Copy by making a full slice
shoplist is ['mango', 'carrot', 'banana']
mylist is ['carrot', 'banana']
执行过程：
程序的注释部分已经说的很明白，值得注意的是如果你想对一个list或者类似的sequence对象或其他的复杂做复制操作的话(像integer这样的简单对象不需要考虑这个问题)，你就要使用slicing操作来完成复制。如果仅仅把一个变量名赋值给另外一个变量名，那么这两个变量将指向同一个对象。如果你没有注意到这一点，那么将会给你带来不必要的麻烦。
说明：该文章从 A byte of Python v1.92 for Python3.0翻译而来，望指正