Python Lists
Lists are one of the most important and widely used data structures in Python.
They allow you to store multiple values in a single variable, and they are ordered, mutable, and flexible.
Lists are used everywhere—from basic programs to real-world applications.
What Is a List?
A list is a collection that:
- Is ordered
- Is mutable (can be changed)
- Allows duplicate values
- Can store different data types
python
numbers = [1, 2, 3, 4]
print(numbers)
python
mixed = [1, "Python", 3.14, True]
print(mixed)
Creating a List
Using Square Brackets
python
fruits = ["apple", "banana", "cherry"]
print(fruits)
python
empty_list = []
print(empty_list)
Using list() Constructor
python
numbers = list((1, 2, 3))
print(numbers)
python
letters = list("Python")
print(letters)
Access List Items (Indexing)
List items are indexed starting from
0.python
colors = ["red", "green", "blue"]
print(colors[0])
python
print(colors[2])
python
print(colors[-1])
Change List Items (Mutable Nature)
python
numbers = [1, 2, 3]
numbers[0] = 10
print(numbers)
python
colors = ["red", "green", "blue"]
colors[1] = "yellow"
print(colors)
List Length
python
numbers = [1, 2, 3, 4]
print(len(numbers))
python
print(len([]))
Check Item Exists
python
fruits = ["apple", "banana", "cherry"]
print("apple" in fruits)
python
print("mango" not in fruits)
Loop Through a List
python
colors = ["red", "green", "blue"]
for color in colors:
print(color)
python
for i in range(len(colors)):
print(colors[i])
Add Items to a List
append() – Add at the End
python
numbers = [1, 2, 3]
numbers.append(4)
print(numbers)
insert() – Add at Specific Index
python
numbers = [1, 3, 4]
numbers.insert(1, 2)
print(numbers)
Remove Items from a List
remove() – Remove by Value
python
fruits = ["apple", "banana", "cherry"]
fruits.remove("banana")
print(fruits)
pop() – Remove by Index
python
fruits = ["apple", "banana", "cherry"]
fruits.pop(1)
print(fruits)
python
fruits.pop()
del Keyword
python
numbers = [1, 2, 3]
del numbers[1]
print(numbers)
List Slicing
python
numbers = [0, 1, 2, 3, 4, 5]
print(numbers[1:4])
python
print(numbers[:3])
python
print(numbers[::2])
Copy a List (Important)
Wrong Way (Reference Copy)
python
a = [1, 2, 3]
b = a
b.append(4)
print(a)
Correct Way (Actual Copy)
python
a = [1, 2, 3]
b = a.copy()
b.append(4)
print(a)
print(b)
python
c = list(a)
Sort a List
python
numbers = [3, 1, 4, 2]
numbers.sort()
print(numbers)
python
numbers.sort(reverse=True)
Reverse a List
python
numbers = [1, 2, 3]
numbers.reverse()
print(numbers)
List Methods (Quick Overview)
| Method | Description |
|---|---|
append() | Add item |
insert() | Insert at index |
remove() | Remove value |
pop() | Remove index |
sort() | Sort list |
reverse() | Reverse list |
copy() | Copy list |
clear() | Remove all items |
count() | Count occurrences |
index() | Find index |
List with Mixed Data Types
python
data = [10, "Python", True, 3.14]
print(data)
Common Mistakes
Modifying List While Iterating
python
nums = [1, 2, 3]
for n in nums:
nums.remove(n)
print(nums)
Summary
- Lists store multiple values
- Ordered and mutable
- Support indexing and slicing
- Allow duplicates
- Rich set of methods
- Very commonly used in Python programs
Practice
- Create a list of numbers and modify it
- Add and remove elements
- Copy a list safely
- Sort and reverse a list