Python 2.x list 超新手常犯的錯誤

a = [1, 2, 3]

b = a

是將b指向 和a共用的 [1,2,3]

如果b用copy a list value成一個獨立的list，請用

b = list(a)

或是用 
copy.deepcopy():

• If the list contains objects and you want to copy them as well, use generic copy.deepcopy():
  

  import copy
  new_list = copy.deepcopy(old_list)

  Obviously the slowest and most memory-needing method, but sometimes unavoidable.

詳參：

Python: copying a list the right way

An Introduction to Python Lists

How to clone a list in python?