copy() method to get a copy of a list

my_list=['Alex','Ronald','John','Ronald','Ronn']
my_list2=my_list.copy()
print(my_list2)

['Alex', 'Ronald', 'John', 'Ronald', 'Ronn']

my_list=['Alex','Ronald','John','Ronald','Ronn']
my_list2=my_list[:]
print(my_list2)

['Alex', 'Ronald', 'John', 'Ronald', 'Ronn']

Example 2: Shallow vs Deep Copy of Nested Lists

import copy

original = [1, [2, 3], 4]
shallow = original.copy()
deep = copy.deepcopy(original)

original[1][0] = 'X'

print("Shallow:", shallow)   # ['1', ['X', 3], 4]
print("Deep:", deep)         # [1, [2, 3], 4]

• This shows that shallow copy cannot isolate changes in nested lists, while deep copy does.

Example 3: Copying Large Lists Efficiently

import time

big = list(range(1000000))

start = time.time()
big_copy = big.copy()
print("copy() took:", time.time() - start)

start2 = time.time()
slice_copy = big[:]
print("slice took:", time.time() - start2)

• Compares performance of list.copy() vs slicing for large lists.
• Good for readers who plan to use copying in data‑heavy situations.

Example 4: Copying Custom Objects Implementing __copy__

class MyList(list):
    def __copy__(self):
        print("Using custom copy")
        return MyList(self[:])

orig = MyList([10, 20, 30])
c = orig.copy()
print(type(c), c)

• Illustrates when list subclass overrides the behavior of copy.

Edge Cases & Best Practices

• What happens when list has mutable items (nested lists, dicts)? Use deep copy for full independence.
• Copying empty list returns a new empty list.
• Changing the original list does not affect a list made via copy() for top‑level elements.
• Good to mention memory cost when copying very large lists.

Subhendu Mohapatra

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