Working with Python Lists

What is a List in Python?

A list in Python is one of the most commonly used data structures. Think of it as a collection of items that can be stored in a specific order.

Key Characteristics

Ordered — Items have a specific order, so each item has an index starting from 0. The last element always have index -1.

Mutable —Unlike strings, Lists are mutable. You can change, add, or remove items after the list is created

Heterogeneous — A list can contain different data types: numbers, strings, booleans, other lists, etc.

Dynamic — You can grow or shrink the list as needed.

Creating Lists

# Empty list
empty_list = []

# List of numbers
numbers = [10, 20, 30, 40]

# List of strings
fruits = ["apple", "banana", "cherry"]

# Mixed data types
mixed = [1, "two", 3.5, True]

# List of lists
nested = [[1,2], [3,4], [5,6]]

Accessing Elements

Elements can be accessed via Index. As mentioned first element always have index 0 and the last element have index -1.

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

fruits[0]   # "apple" → first element
fruits[-1]  # "cherry" → last element
fruits[0:2] # ["apple", "banana"] → slicing
fruits[4]   # Error -> cannot access element 

Why Lists Are Useful

Lists can Store collections of related data

Iterate easily using loops

Perform mathematical or logical operations

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Can be nested (list of lists) for tables or matrices.

# A shopping list
shopping = ["milk", "bread", "eggs"]

# Add an item
shopping.append("butter")

# Remove an item
shopping.remove("bread")

# Loop through items
for item in shopping:
    print(item)

# Output:
# milk
# eggs
# butter
"milk" in shopping   #True

# Find all the methods in List
dir(list) 

#Clear the list 
shopping.clear() 

#extend
shopping.extend(['jam', 'oats',])

#Count
numbers=[1,2,3,3,4,4,5,6,6,7,8,8]
print(numbers.count(4))
#2

# copy
new_numbers=numbers.copy()
print(new_numbers)

Adding Items

fruits = ["apple", "banana", "cherry"]
fruits.append("orange")        # Add at end
fruits.insert(1, "kiwi")       # Add at index 1
fruits.extend(["mango","grape"])  # Add multiple

Removing Items

fruits.remove("banana")        # Remove first occurrence
fruits.pop()                   # Remove last
fruits.pop(1)                  # Remove index 1
fruits.clear()                 # Remove all items

Searching & Counting

fruits.index("cherry")         # Get index
fruits.count("apple")          # Count occurrences

Copying

copy_fruits = fruits.copy()    # Shallow copy
same_list = fruits             # References same list

Common Operations / Functions

len(fruits)       # Number of items
sum(numbers)      # Sum of numbers
min(numbers)      # Minimum
max(numbers)      # Maximum

List Comprehensions (Very Useful)

squares = [x**2 for x in range(5)]           # [0,1,4,9,16]
even = [x for x in range(10) if x % 2 == 0]  # [0,2,4,6,8]

Iterating Over Lists

for fruit in fruits:
    print(fruit)

for i, fruit in enumerate(fruits):
    print(i, fruit)

Combining & Repeating

a = [1,2]
b = [3,4]
c = a + b           # [1,2,3,4]
d = a * 3           # [1,2,1,2,1,2]

Slicing Shortcuts

numbers[::-1]       # Reverse list
numbers[::2]        # Every second item
numbers[-3:]        # Last 3 items
numbers[:-3]        # All except last 3

Quick Reference Table for List Methods

 Method               | Description                                        |
--------------------  | -------------------------------------------------- |
 `append(x)`          | Add `x` at the end                                 |
 `insert(i,x)`        | Insert `x` at index `i`                            |
 `extend(iterable)`   | Add all items from another iterable                |
 `remove(x)`          | Remove first occurrence of `x`                     |
 `pop([i])`           | Remove and return item at index `i` (default last) |
 `clear()`            | Remove all items                                   |
 `index(x)`           | Return index of first occurrence                   |
 `count(x)`           | Count occurrences of `x`                           |
 `sort()`             | Sort ascending                                     |
 `sort(reverse=True)` | Sort descending                                    |
 `reverse()`          | Reverse list in place                              |
 `copy()`             | Return a shallow copy                              |