Day 14: Confusing append() vs extend()

 

🐍Python Mistakes Everyone Makes ❌

Day 14: Confusing append() vs extend()

append() and extend() may look similar, but they behave very differently.

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❌ The Mistake

items = [1, 2, 3]
items.append([4, 5])
print(items)

Output:

[1, 2, 3, [4, 5]]

The entire list is added as a single element.

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✅ The Correct Way

items = [1, 2, 3]
items.extend([4, 5])
print(items)

Output:

[1, 2, 3, 4, 5]

Each element is added individually.

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❌ Why This Fails?

append() adds the whole object as one item.
It does not unpack or loop through the elements.

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✔ Key Differences

• append() → adds one element

• extend() → adds multiple elements

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🧠 Simple Rule to Remember

• append() keeps the list nested

• extend() flattens the iterable