Python Tutorial

Python Add List Items

append() adds at the end, insert() adds at an index, extend() adds all items from another iterable.

append()

Add an item to the end of the list.

thislist = ["apple", "banana", "cherry"]
thislist.append("orange")
print(thislist)

insert()

Insert at a specified index. Existing items shift right.

thislist = ["apple", "banana", "cherry"]
thislist.insert(1, "orange")
print(thislist)

extend()

Append elements from another list, tuple, set, or any iterable.

thislist = ["apple", "banana", "cherry"]
tropical = ["mango", "pineapple"]
thislist.extend(tropical)
print(thislist)

📘 Real-World Deep Dive

Adding items to a list — append, extend, insert, plus the trade-offs of <code>+</code>, <code>+=</code>, and slicing assignment — shows up everywhere. Picking the right one is the difference between O(1) and O(n).

Real-Life Scenario

Two ways to ingest a stream into a list: append one-by-one, vs. extend with a slice. Show the same end result, distinct allocations.

Real-Life Example

a: list[int] = []
for x in range(5):
    a.append(x)                     # O(1) each; keeps existing backing storage
print("a:", a)

b: list[int] = []
b.extend(range(5))                 # single C-level call; newer memory
print("b:", b)

# Inserting in the middle
a.insert(2, 99)                    # O(n) due to shift
print("after insert:", a)

# '+' vs '+=' semantics
c = a + [100, 101]                 # new list
print("c (new):", c, "id different from a:", id(c) != id(a))
a += [200, 201]                    # in-place extend
print("a (in-place):", a, "id unchanged:", id(a) == a.__hash__())

Expected Output

a: [0, 1, 2, 3, 4]
b: [0, 1, 2, 3, 4]
after insert: [0, 1, 99, 2, 3, 4]
c (new): [0, 1, 99, 2, 3, 4, 100, 101] id different from a: True
a (in-place): [0, 1, 99, 2, 3, 4, 200, 201] id unchanged: True

Common mistakes

a = a + b creates a new list; a += b extends in place (for list).
Inserting at the head of a large list is O(n); consider deque.appendleft.
Repeated list.append(other_list) gives a nested list — use extend instead.

🚀 Performance & Best Practices

extend(iterable) is C-fast and often beats append in a loop.
Building a list then joining is faster than concatenating strings in a loop.
Pre-allocate with [None] * n if you know the size up front.

🧪 Try It Yourself

Refactor append in a hot loop to extend with a generator and benchmark.
Implement push_many(xs, i, items) that splices items at position i.
Profile list vs. collections.deque for a queue with 1 M push/pops.

FAQ: Python Add List Items

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What is Python Add List Items?

Python Add List Items is a Python Tutorial lesson that explains add items to list python in Python. append() adds at the end, insert() adds at an index, extend() adds all items from another iterable. Copy the samples and run them in the Python editor. It is written for beginners who want a clear definition and working examples.

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