Shallow Copy & Deep Copy in Python (5)

#python #dictionary #shallowcopy #deepcopy

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*Memos:

My post explains the shallow and deep copy of a list.
My post explains the shallow and deep copy of a tuple.
My post explains the shallow copy of the set with a tuple.
My post explains the shallow and deep copy of the set with an iterator.
My post explains the shallow and deep copy of an iterator.
My post explains variable assignment.

Normal Copy:

*Memos:

v1 and v2 refer to the same shallow and deep dictionary.
is keyword can check if v1 and v2 refer to the same dictionary.

     #### Shallow dictionary ####
#    ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓           ↓
v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = v1          #   ↑↑↑↑↑↑↑↑↑↑↑
                 # Deep dictionary
print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # True True

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'V_A', 'd': {'k': 'V_B'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

Shallow Copy:

copy() can do shallow copy as shown below:

*Memos:

v1 and v2 refer to the different shallow dictionaries.
v1 and v2 refer to the same deep dictionary.

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = v1.copy() # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False True

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'V_B'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

The below with copy() which can do shallow copy is equivalent to the above:

from copy import copy

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = copy(v1) # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False True

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'V_B'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

The below with dict() which can do shallow copy is equivalent to the above:

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = dict(v1) # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False True

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'V_B'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

Deep Copy:

deepcopy() can do deep copy as shown below:

*Memos:

v1 and v2 refer to the different shallow and deep dictionaries.
deepcopy() should be used because it's safe, doing copy deeply.

from copy import deepcopy

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = deepcopy(v1) # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False False

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

The below with copy() which can do shallow copy is equivalent to the above:

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = v1.copy() # Here
v2['d'] = v1['d'].copy() # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False False

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

The below with copy() which can do shallow copy is equivalent to the above:

from copy import copy

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = copy(v1) # Here
v2['d'] = copy(v1['d']) # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False False

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

The below with dict() which can do shallow copy is equivalent to the above:

v1 = {'k':'v_a', 'd':{'k':'v_b'}}
v2 = dict(v1) # Here
v2['d'] = dict(v1['d']) # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v1 is v2, v1['d'] is v2['d']) # False False

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
          #       ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'v_b'}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B'}}
          #       ↑↑↑↑↑             ↑↑↑↑↑

Additionally, the below is a 3D dictionary:

from copy import deepcopy

v1 = {'k':'v_a', 'd':{'k':'v_b', 'd':{'k':'v_c'}}}
v2 = deepcopy(v1) # Here

print(v1) # {'k': 'v_a', 'd': {'k': 'v_b', 'd': {'k': 'v_c'}}}
print(v2) # {'k': 'v_a', 'd': {'k': 'v_b', 'd': {'k': 'v_c'}}}
print(v1 is v2, v1['d'] is v2['d'], v1['d']['d'] is v2['d']['d'])
# False False False

v2['k'] = 'V_A'
v2['d']['k'] = 'V_B'
v2['d']['d']['k'] = 'V_C'
          #       ↓↓↓↓↓             ↓↓↓↓↓             ↓↓↓↓↓
print(v1) # {'k': 'v_a', 'd': {'k': 'v_b', 'd': {'k': 'v_c'}}}
print(v2) # {'k': 'V_A', 'd': {'k': 'V_B', 'd': {'k': 'V_C'}}}
          #       ↑↑↑↑↑             ↑↑↑↑↑             ↑↑↑↑↑

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Shallow Copy & Deep Copy in Python (5)

Normal Copy:

Shallow Copy:

Deep Copy:

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