Python Basics — List Methods

List Methods

Python lists come with powerful built-in methods for adding, removing, sorting, and searching.

Adding Elements

append() — Add to End

fruits = ["apple", "banana"]
fruits.append("cherry")
print(fruits)  # ['apple', 'banana', 'cherry']

extend() — Add Multiple Elements

fruits = ["apple", "banana"]
fruits.extend(["cherry", "date"])
print(fruits)  # ['apple', 'banana', 'cherry', 'date']

# extend() vs append() with a list
fruits = ["apple"]
fruits.append(["b", "c"])   # Adds the list as ONE element
print(fruits)  # ['apple', ['b', 'c']]

fruits = ["apple"]
fruits.extend(["b", "c"])   # Adds each element individually
print(fruits)  # ['apple', 'b', 'c']

insert() — Add at Position

fruits = ["apple", "cherry"]
fruits.insert(1, "banana")  # Insert at index 1
print(fruits)  # ['apple', 'banana', 'cherry']

fruits.insert(0, "avocado")  # Insert at beginning
print(fruits)  # ['avocado', 'apple', 'banana', 'cherry']

Removing Elements

remove() — Remove by Value

fruits = ["apple", "banana", "cherry", "banana"]
fruits.remove("banana")  # Removes FIRST occurrence
print(fruits)  # ['apple', 'cherry', 'banana']

# ValueError if not found
# fruits.remove("grape")  # ValueError

pop() — Remove by Index

fruits = ["apple", "banana", "cherry"]

last = fruits.pop()       # Remove and return last item
print(last)               # cherry
print(fruits)             # ['apple', 'banana']

first = fruits.pop(0)     # Remove and return item at index 0
print(first)              # apple
print(fruits)             # ['banana']

clear() — Remove All

fruits = ["apple", "banana", "cherry"]
fruits.clear()
print(fruits)  # []

del — Delete by Index or Slice

fruits = ["apple", "banana", "cherry", "date"]

del fruits[1]      # Delete index 1
print(fruits)      # ['apple', 'cherry', 'date']

del fruits[0:2]    # Delete slice
print(fruits)      # ['date']

Sorting

sort() — Sort In Place

numbers = [3, 1, 4, 1, 5, 9, 2, 6]
numbers.sort()
print(numbers)  # [1, 1, 2, 3, 4, 5, 6, 9]

numbers.sort(reverse=True)
print(numbers)  # [9, 6, 5, 4, 3, 2, 1, 1]

# Sort strings (case-sensitive by default)
words = ["banana", "Apple", "cherry"]
words.sort()
print(words)  # ['Apple', 'banana', 'cherry']

# Case-insensitive sort
words.sort(key=str.lower)
print(words)  # ['Apple', 'banana', 'cherry']

sorted() — Return New Sorted List

numbers = [3, 1, 4, 1, 5]
sorted_nums = sorted(numbers)

print(sorted_nums)  # [1, 1, 3, 4, 5]
print(numbers)       # [3, 1, 4, 1, 5]  (original unchanged)

sort() vs sorted()

Feature	list.sort()	sorted(list)
Returns	None	New sorted list
Modifies original	Yes	No
Works on	Lists only	Any iterable

reverse() — Reverse In Place

fruits = ["apple", "banana", "cherry"]
fruits.reverse()
print(fruits)  # ['cherry', 'banana', 'apple']

Searching

index() — Find Position

fruits = ["apple", "banana", "cherry", "banana"]
print(fruits.index("banana"))     # 1 (first occurrence)
print(fruits.index("banana", 2))  # 3 (search from index 2)

# ValueError if not found
# fruits.index("grape")  # ValueError

count() — Count Occurrences

numbers = [1, 2, 3, 2, 2, 4, 2]
print(numbers.count(2))  # 4
print(numbers.count(5))  # 0

Copying Lists

Shallow Copy

original = [1, 2, 3]

# Three ways to copy
copy1 = original.copy()
copy2 = original[:]
copy3 = list(original)

copy1.append(4)
print(original)  # [1, 2, 3]  (not affected)
print(copy1)     # [1, 2, 3, 4]

Assignment Is NOT Copying

original = [1, 2, 3]
alias = original  # Both point to the SAME list

alias.append(4)
print(original)  # [1, 2, 3, 4]  — original also changed!

List as Stack and Queue

Stack (LIFO — Last In, First Out)

stack = []
stack.append("first")
stack.append("second")
stack.append("third")

print(stack.pop())  # third
print(stack.pop())  # second
print(stack)        # ['first']

Queue (FIFO — First In, First Out)

from collections import deque

queue = deque()
queue.append("first")
queue.append("second")
queue.append("third")

print(queue.popleft())  # first
print(queue.popleft())  # second
print(queue)            # deque(['third'])

Use collections.deque for queues — list.pop(0) is slow (O(n)) because it shifts all elements.

Complete Methods Reference

Method	Description	Returns
append(x)	Add to end	None
extend(iter)	Add all from iterable	None
insert(i, x)	Insert at position	None
remove(x)	Remove first occurrence	None
pop(i)	Remove and return at index	Removed item
clear()	Remove all items	None
sort()	Sort in place	None
reverse()	Reverse in place	None
copy()	Shallow copy	New list
index(x)	Find first index of x	Index
count(x)	Count occurrences of x	Count

Summary

• Add: append(), extend(), insert()
• Remove: remove(), pop(), clear(), del
• Sort: sort() (in-place), sorted() (new list)
• Search: index(), count()
• Copy: .copy(), [:], or list()
• sort() and reverse() modify the list and return None
• Assignment (=) creates an alias, not a copy

---

Next up: List Slicing →