对python append 与浅拷贝的实例讲解

class Solution(object):
 def combinationSum(self, candidates, target):
 """
 :type candidates: List[int]
 :type target: int
 :rtype: List[List[int]]
 """
 result,temp = [],[]
 self.combinationSumRecu(sorted(candidates),result,0,temp,target)
 return result

 def combinationSumRecu(self, candidates, result, start, temp, target):
 if target == 0:
  result.append(temp) # 注意此处不能直接append(temp)，否则是浅拷贝，之后temp.pop()时会将result中的数也pop出来
 while start < len(candidates) and candidates[start]<=target:
  temp.append(candidates[start])
  self.combinationSumRecu(candidates, result, start, temp,target-candidates[start])
  temp.pop()
  start += 1

if __name__ == '__main__':
 print Solution().combinationSum([2,3,6,7],7)

if target == 0: 
 print type(temp),temp,result 
 result.append(temp) 

<type 'list'> [2, 2, 3] []
<type 'list'> [7] [[7]]

if target == 0: 
 print type(temp),temp,result 
 result.append(list(temp)) 

<type 'list'> [2, 2, 3] []
<type 'list'> [7] [[7]]

a = [1,2] 
b = [3,4] 
a.append(b) 
print a 
b.pop() 
print a 

[1, 2, [3, 4]]
[1, 2, [3]]