看看官方的讲解：
Python v2.7.2 documentation » The Python Standard Library » 8. Data Types » 8.17. copy — Shallow and deep copy operations
copy.copy(x)
Return a shallow copy of x.
copy.deepcopy(x)
Return a deep copy of x.
The difference between shallow and deep copying is only relevant for compound objects (objects that contain other objects, like lists or class instances):
A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.
A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.
Shallow copies of dictionaries can be made using dict.copy(), and of lists by assigning a slice of the entire list, for example, copiedlist = originallist[:].
举例（IPython）：
先看看浅复制(Shallow Copy)：
In [1]: import copy
In [2]: a = [1,2,3,[4,5,6,[7,8,9]]]
In [3]: b = copy.copy(a)
In [4]: print a
[1, 2, 3, [4, 5, 6, [7, 8, 9]]]
In [5]: print b
[1, 2, 3, [4, 5, 6, [7, 8, 9]]]
In [6]: b[0] = 10
In [7]: print b
[10, 2, 3, [4, 5, 6, [7, 8, 9]]]
In [8]: print a
[1, 2, 3, [4, 5, 6, [7, 8, 9]]] # a没有变化
In [9]: b[3][0] = 11
In [10]: print b
[10, 2, 3, [11, 5, 6, [7, 8, 9]]]
In [11]: print a
[1, 2, 3, [11, 5, 6, [7, 8, 9]]] # a有变化
再来看看深复制(Deep Copy)：
In [1]: import copy
In [2]: a = [1,2,3,[4,5,6,[7,8,9]]]
In [3]: b = copy.deepcopy(a)
In [4]: print a
[1, 2, 3, [4, 5, 6, [7, 8, 9]]]
In [5]: print b
[1, 2, 3, [4, 5, 6, [7, 8, 9]]]
In [6]: b[3][0] = 11
In [7]: print b
[1, 2, 3, [11, 5, 6, [7, 8, 9]]]
In [8]: print a
[1, 2, 3, [4, 5, 6, [7, 8, 9]]] # a没变化
三篇参考：
http://docs.python.org/library/copy.html
http://blog.csdn.net/sharkw/article/details/1934090
http://ebkk.blog.163.com/blog/static/19413508520097266592180/