--- id: python-list title: List in Python sidebar_label: List in Python #displays in sidebar sidebar_position: 8 tags: [ Python, List in Python, Introduction of python, Python Syntax, Variables, Operators, Type Casting, String ] --- # Lists in Python A **List** in Python is a data structure that allows you to store multiple items in a single variable. Lists are **ordered**, **mutable**, and **can contain elements of different data types**. ## Creating a List You create a list using square brackets `[]`: ```python # Empty List empty_list = [] # List of Integers numbers = [1, 2, 3, 4, 5] # List of Strings fruits = ["apple", "banana", "cherry"] # Mixed Data Types mixed = [1, "hello", 3.14, True] ```` ## Indexing **Indexing** means accessing elements by their position. * Index starts from **0** in Python: ```python fruits = ["apple", "banana", "cherry"] print(fruits[0]) # apple print(fruits[1]) # banana print(fruits[2]) # cherry ``` * Negative indexing starts from the end: ```python print(fruits[-1]) # cherry print(fruits[-2]) # banana print(fruits[-3]) # apple ``` ## Slicing **Slicing** lets you extract a sublist: ```python numbers = [10, 20, 30, 40, 50] print(numbers[1:4]) # [20, 30, 40] print(numbers[:3]) # [10, 20, 30] print(numbers[2:]) # [30, 40, 50] print(numbers[-3:-1]) # [30, 40] ``` **Syntax:** ``` list[start:stop:step] ``` **Example with step:** ```python print(numbers[::2]) # [10, 30, 50] ``` ## Modifying Elements Lists are **mutable**, which means you can change their contents: ```python fruits = ["apple", "banana", "cherry"] fruits[1] = "mango" print(fruits) # ['apple', 'mango', 'cherry'] ``` ## List Methods Python provides many built-in methods for lists: | Method | Description | | -------------- | ----------------------------------------------------- | | `append(x)` | Adds an item to the end of the list | | `insert(i, x)` | Inserts an item at a specific index | | `extend(iter)` | Adds all elements from another iterable | | `remove(x)` | Removes the first occurrence of the item | | `pop([i])` | Removes and returns the item at the given index | | `clear()` | Removes all elements | | `index(x)` | Returns the index of the first occurrence of the item | | `count(x)` | Counts how many times the item appears | | `sort()` | Sorts the list in ascending order | | `reverse()` | Reverses the list | | `copy()` | Returns a shallow copy of the list | --- ### Examples #### append() ```python nums = [1, 2, 3] nums.append(4) print(nums) # [1, 2, 3, 4] ``` #### insert() ```python nums.insert(1, 100) print(nums) # [1, 100, 2, 3, 4] ``` #### extend() ```python nums.extend([5, 6]) print(nums) # [1, 100, 2, 3, 4, 5, 6] ``` #### remove() and pop() ```python nums.remove(100) print(nums) # [1, 2, 3, 4, 5, 6] nums.pop() # Removes the last element print(nums) # [1, 2, 3, 4, 5] nums.pop(2) # Removes index 2 print(nums) # [1, 2, 4, 5] ``` ## Iterating Through a List **Using a for loop:** ```python fruits = ["apple", "banana", "cherry"] for item in fruits: print(item) ``` **Output:** ``` apple banana cherry ``` **Using indices:** ```python for i in range(len(fruits)): print(i, fruits[i]) ``` ## Membership Test Check whether an item exists in the list: ```python print("apple" in fruits) # True print("mango" not in fruits) # True ``` ## Nested Lists Lists can contain other lists: ```python matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ] print(matrix[0]) # [1, 2, 3] print(matrix[1][2]) # 6 ``` ## List Comprehensions A **concise way** to create new lists: ```python squares = [x**2 for x in range(1, 6)] print(squares) # [1, 4, 9, 16, 25] ``` **With a condition:** ```python even = [x for x in range(10) if x % 2 == 0] print(even) # [0, 2, 4, 6, 8] ``` ## Copying Lists Be careful! Assigning directly creates a reference: ```python a = [1, 2, 3] b = a b.append(4) print(a) # [1, 2, 3, 4] ``` To create an **independent copy:** ```python c = a.copy() c.append(5) print(a) # [1, 2, 3, 4] print(c) # [1, 2, 3, 4, 5] ``` ## Conclusion Python Lists are a **powerful and flexible** data structure used everywhere—from collecting and processing data to building complex programs. Practice using list methods and experiment to become confident.