Copy ＆ Deepcopy

• copy()用来复制列表或字典里的值，并不是复制引用。以下代码中，a和a_copy是两个不同的列表，两者互不影响。
• deepcopy()可以复制列表里包含的子列表。以下代码中可以看出，copy()只拷贝了单层列表，而deepcopy()拷贝了嵌套列表。

• import copy
  a = [1,2,3]
  b = [1, 2, [3, 4]]
  a_copy = a.copy()
  a_deepcopy = copy.deepcopy(a)
  b_copy = b.copy()
  b_deepcopy = copy.deepcopy(b)
  print(a == a_copy, a==a_deepcopy, a_copy==a_deepcopy)
  print(a is a_copy, a is a_deepcopy, a_copy is a_deepcopy)
  # Output: True True True
          # False False False
  
  print("a:",a, "a_copy:",a_copy, "a_deepcopy:",a_deepcopy)
  print("b:",b, "b_copy:",b_copy, "b_deepcopy:",b_deepcopy)
  # Output: a: [1, 2, 3] 
          # a_copy: [1, 2, 3] 
          # a_deepcopy: [1, 2, 3]
          # b: [1, 2, [3, 4]] 
          # b_copy: [1, 2, [3, 4]] 
          # b_deepcopy: [1, 2, [3, 4]]
  
  a[0] = 4
  a.append(5)
  b[2][0] = "c"
  b.append(3)
  b.append([7,8])
  print("a:",a, "a_copy:",a_copy, "a_deepcopy:",a_deepcopy)
  print("b:",b, "b_copy:",b_copy, "b_deepcopy:",b_deepcopy)
  # Output:a: [4, 2, 3, 5] 
          # a_copy: [1, 2, 3] 
          # a_deepcopy: [1, 2, 3]
          # b: [1, 2, ['c', 4], 3, [7, 8]] 
          # b_copy: [1, 2, ['c', 4]] 
          # b_deepcopy: [1, 2, [3, 4]]

  参考