- 创建一个对象并给它赋一个变量的时候，这个变量仅仅 引用 那个对象，而不是表示这个对象本身
- 如果想要复制一个列表或者类似的序列或者其他复杂的对象（不是如整数那样的简单 对象 ），那么你必须使用切片操作符来取得拷贝。如果你只是想要使用另一个变量名，两个名称都 引用 同一个对象，那么如果你不小心的话，可能会引来各种麻烦。
# !D:\Python
# 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]
print 'shoplist is',shoplist
print 'mylist', 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', shoplist
print 'mylist', mylist
# notice that now the two list are different
结果：
Simple Assignment
shoplist is ['mango', 'carrot', 'banana']
mylist ['mango', 'carrot', 'banana']
Copy by making a full slice
shoplist ['mango', 'carrot', 'banana']
mylist ['carrot', 'banana']
