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

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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