Shallow and deep copies in Python

1. Lists and dictionaries, directly assigned, are shallow copies, where both sides point to the same address, because Python passes by reference to mutable objects.

>>> a = [1, 2, 3]>>> B =a>>>b[1, 2, 3]>>> A[0] ='Apple'>>>a['Apple', 2, 3]>>>b['Apple', 2, 3]>>> >>> >>> dic = {'a':'Apple','b':'Banbana'}>>> Dic2 =DiC>>>dic2{'a':'Apple','b':'Banbana'}>>> dic['b'] ='Blueberry'>>>dic{'a':'Apple','b':'Blueberry'}>>>dic2{'a':'Apple','b':'Blueberry'}

2. For a non-nested list, use a full slice [:], the factory function list (), or copy.copy () are deep copies.

 >>> A = [1, 2, 3 >>> b = >>> c = a[:]  >>> import   copy  >>> d = Copy.copy (a)  > >> >>> a[0] =    '  >>>

3. For non-nested dictionaries, use the Factory function Dict (), or copy.copy () are deep copies.

>>> dic = {'a':'Apple','b':'Banana'}>>> Dic2 =dict (DIC)>>>ImportCopy>>> DIC3 =copy.copy (DIC)>>> >>> dic['b'] ='Blueberry'>>>dic{'a':'Apple','b':'Blueberry'}>>>dic2{'a':'Apple','b':'Banana'}>>>dic3{'a':'Apple','b':'Banana'}

4. For nested lists, nested dictionaries can only use copy.deepcopy () to implement deep copies.

>>>ImportCopy>>> >>> A = [1, 2, ['Apple']]>>> B =Copy.deepcopy (a)>>> A[2][0] ='Watermelon'>>>a[1, 2, ['Watermelon']]>>>b[1, 2, ['Apple']]>>> >>> >>> dic = {'a':'Apple','b': {'B1':'Banana','B2':'Blueberry'}}>>> Dic2 =copy.deepcopy (DIC)>>> dic['b']['B1'] ='Bukeneng'>>>dic{'a':'Apple','b': {'B1':'Bukeneng','B2':'Blueberry'}}>>>dic2{'a':'Apple','b': {'B1':'Banana','B2':'Blueberry'}}

5. For tuples that Nest mutable objects, only copy.deepcopy () implements a deep copy.

>>>ImportCopy
>>>>>> T = (1, 2, ['Apple'])>>> t2 =T>>> t3 =tuple (t)>>> T4 =copy.copy (t)>>> T5 =copy.deepcopy (t)>>> >>> T[2][0] ='Watermelon'>>>T (1, 2, ['Watermelon'])>>>T2 (1, 2, ['Watermelon'])>>>T3 (1, 2, ['Watermelon'])>>>T4 (1, 2, ['Watermelon'])>>>T5 (1, 2, ['Apple'])

Finish.

Shallow and deep copies in Python