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Super Kai (Kazuya Ito)
Super Kai (Kazuya Ito)

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Shallow Copy & Deep Copy in Python (3)

#python #set #shallowcopy #deepcopy

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*Memos:

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

<A set with a tuple>

A set can have a tuple and iterator but cannot have a set, list and dictionary. *The same tuple is always referred to because a tuple cannot be copied according to the experiments so for the set with a tuple, only shallow copy is possible.

Normal Copy:

*Memos:

  • A and B refer to the same shallow set and deep tuple.
  • is keyword can check if v1 and v2 refer to the same set or tuple. 
# Shallow set # ↓ ↓ A = {('a',)} # ↑↑↑↑↑↑ Deep tuple B = A print(A) # {('a',)} print(B) # {('a',)} print(A is B) # True  print(A.pop()) # ('a',) print(B.pop()) # KeyError: 'pop from an empty set'
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Shallow Copy:

copy() can do shallow copy as shown below:

*Memos:

  • A and B refer to different shallow sets.
  • A and B refer to the same deep tuple. 
A = {('a',)} B = A.copy() # Here  print(A) # {('a',)} print(B) # {('a',)} print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # ('a',) print(v2) # ('a',) print(v1 is v2) # True
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The below with copy() which can do shallow copy is equivalent to the above:

from copy import copy A = {('a',)} B = copy(A) # Here  print(A) # {('a',)} print(B) # {('a',)} print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # ('a',) print(v2) # ('a',) print(v1 is v2) # True
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The below with deepcopy() which can do deep copy is equivalent to the above. *deepcopy() should be used because it's safe, doing copy deeply:

from copy import deepcopy A = {('a',)} B = deepcopy(A) # Here  print(A) # {('a',)} print(B) # {('a',)} print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # ('a',) print(v2) # ('a',) print(v1 is v2) # True
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The below with set() which can do shallow copy is equivalent to the above:

A = {('a',)} B = set(A) # Here  print(A) # {('a',)} print(B) # {('a',)} print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # ('a',) print(v2) # ('a',) print(v1 is v2) # True
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Additionally, the below is the 3D set with a 2D tuple:

from copy import deepcopy A = {(('a',),)} B = deepcopy(A) # Here  print(A) # {(('a',),)} print(B) # {(('a',),)} print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # (('a',),) print(v2) # (('a',),) print(v1[0]) # ('a',) print(v2[0]) # ('a',) print(v1 is v2, v1[0] is v2[0]) # True True
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