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

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Shallow Copy & Deep Copy in Python (4)

#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 copy of the set with a tuple.
  • 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 an iterator>

A set can have a tuple and iterator but cannot have a set, list and dictionary.

<Normal Copy>:

*Memos:

  • A and B refer to the same shallow set and deep iterator.
  • is keyword can check if v1 and v2 refer to the same set or iterator. 
 # Shallow set # # ↓ ↓ A = {iter(['a'])} # ↑↑↑↑↑↑↑↑↑  # Deep iterator # B = A print(A) # {<list_iterator object at 0x000001F95F9C6410>} print(B) # {<list_iterator object at 0x000001F95F9C6410>} print(A is B) # True  v = B.pop() print(v) # <list_iterator object at 0x000001F95F9C6410> print(A) # set() print(B) # 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 iterator. 
A = {iter(['a'])} B = A.copy() # Here  print(A) # {<list_iterator object at 0x000001F9606954E0>} print(B) # {<list_iterator object at 0x000001F9606954E0>} print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # <list_iterator object at 0x000001F9606954E0> print(v2) # <list_iterator object at 0x000001F9606954E0> print(v1 is v2) # True  print(next(v1)) # a print(next(v2)) # StopIteration:
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The below with copy() which can do shallow copy is equivalent to the above:

from copy import copy A = {iter(['a'])} B = copy(A) # Here  print(A) # {<list_iterator object at 0x000001F95F9CD510>} print(B) # {<list_iterator object at 0x000001F95F9CD510>}  print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # <list_iterator object at 0x000001F95F9CD510> print(v2) # <list_iterator object at 0x000001F95F9CD510> print(v1 is v2) # True  print(next(v1)) # a print(next(v2)) # StopIteration:
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The below with set() which can do shallow copy is equivalent to the above:

A = {iter(['a'])} B = set(A) # Here  print(A) # {<list_iterator object at 0x000001F9605E3730>} print(B) # {<list_iterator object at 0x000001F9605E3730>}  print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # <list_iterator object at 0x000001F9605E3730> print(v2) # <list_iterator object at 0x000001F9605E3730> print(v1 is v2) # True  print(next(v1)) # a print(next(v2)) # StopIteration:
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<Deep Copy>:

deepcopy() can do deep copy:

*Memos:

  • A and B refer to the different shallow sets and deep iterators.
  • deepcopy() should be used because it's safe, doing copy deeply. 
from copy import deepcopy A = {iter(['a'])} B = deepcopy(A) # Here  print(A) # {<list_iterator object at 0x000001F96065DE40>} print(B) # {<list_iterator object at 0x000001F960695CC0>}  print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # <list_iterator object at 0x000001F96065DE40> print(v2) # <list_iterator object at 0x000001F960695CC0> print(v1 is v2) # False  print(next(v1)) # a print(next(v2)) # a
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The below with copy() and copy() which can do shallow copy is equivalent to the above:

from copy import copy A = {iter(['a'])} B = A.copy() # Here  print(A) # {<list_iterator object at 0x000001F9604F6410>} print(B) # {<list_iterator object at 0x000001F9604F6410>}  print(A is B) # False  v1 = copy(A.pop()) # Here v2 = copy(B.pop()) # Here  print(v1) # <list_iterator object at 0x000001F9604F7910> print(v2) # <list_iterator object at 0x000001F9605E3190> print(v1 is v2) # False  print(next(v1)) # a print(next(v2)) # a
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The below with set() and copy() which can do shallow copy is equivalent to the above:

from copy import copy A = {iter(['a'])} B = set(A) # Here  print(A) # {<list_iterator object at 0x000001F95F9BDF90>} print(B) # {<list_iterator object at 0x000001F95F9BDF90>}  print(A is B) # False  v1 = copy(A.pop()) # Here v2 = copy(B.pop()) # Here  print(v1) # <list_iterator object at 0x000001F96065DFF0> print(v2) # <list_iterator object at 0x000001F96065D360> print(v1 is v2) # False  print(next(v1)) # a print(next(v2)) # a
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Additionally, the below is the 3D set with a 2D iterator:

from copy import deepcopy A = {iter([iter(['a'])])} B = deepcopy(A) # Here  print(A) # {<list_iterator object at 0x0000029DDF277B20>} print(B) # {<list_iterator object at 0x0000029DE0049210>}  print(A is B) # False  v1 = A.pop() v2 = B.pop() print(v1) # <list_iterator object at 0x0000029DDF277B20> print(v2) # <list_iterator object at 0x0000029DE0049210> print(v1 is v2) # False  v3 = next(v1) v4 = next(v2) print(next(v3)) # a print(next(v4)) # a print(v3 is v4) # False
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