List Methods & Operations
Python provides powerful built-in methods to add, remove, search, and organize items inside a list.
Adding Items (append, insert, extend)
.append(item)adds one item to the very end of the list..insert(index, item)inserts an item at a specific position, shifting the rest to the right..extend(another_list)combines two lists into one.
fruits = ["apple", "banana"]
# Add to the end
fruits.append("orange")
print(fruits) # Output: ['apple', 'banana', 'orange']
# Insert at the beginning (index 0)
fruits.insert(0, "mango")
print(fruits) # Output: ['mango', 'apple', 'banana', 'orange']
Removing Items (remove, pop, clear)
.remove(value)deletes the first matching item by its name/value..pop(index)removes and returns the item at that position. If you leave out the index,.pop()removes the very last item..clear()empties the entire list.
fruits = ["apple", "banana", "orange", "banana"]
# Remove the first "banana"
fruits.remove("banana")
print(fruits) # Output: ['apple', 'orange', 'banana']
# Pop the last item
last_fruit = fruits.pop()
print(f"Removed: {last_fruit}") # Output: Removed: banana
print(fruits) # Output: ['apple', 'orange']
Searching and Counting (index, count, len)
len(my_list)tells you the total number of items..count(value)counts how many times a value appears in the list..index(value)finds the index position of the first matching item.
scores = [10, 20, 30, 20, 10, 20]
print(len(scores)) # Total items: 6
print(scores.count(20)) # How many times 20 appears: 3
print(scores.index(30)) # Position of 30: index 2
Sorting and Reversing (sort, reverse)
.sort()sorts items alphabetically or from lowest to highest number..reverse()flips the list order from back to front.
numbers = [5, 1, 4, 2, 3]
# Sort from smallest to largest
numbers.sort()
print(numbers) # Output: [1, 2, 3, 4, 5]
# Sort from largest to smallest
numbers.sort(reverse=True)
print(numbers) # Output: [5, 4, 3, 2, 1]
Copying a List (copy)
If you want to make a backup copy of a list before changing it, use .copy():
original = ["red", "blue", "green"]
backup = original.copy()
backup.append("yellow")
print(original) # Output: ['red', 'blue', 'green'] (unchanged!)
print(backup) # Output: ['red', 'blue', 'green', 'yellow']
Common Beginner Mistakes
Assigning the result of .append() or .sort() to a variable
# Wrong - .append() and .sort() modify the list directly and return None
numbers = [3, 1, 2]
numbers = numbers.sort()
print(numbers) # Outputs None!
# Right - call the method on a separate line
numbers = [3, 1, 2]
numbers.sort()
print(numbers) # Outputs [1, 2, 3]
Forgetting to copy when duplicating lists
# Wrong - both variables point to the exact same list in memory
list1 = [1, 2, 3]
list2 = list1
list2.append(4)
print(list1) # Outputs [1, 2, 3, 4]!
# Right - use .copy() to create a true separate copy
list1 = [1, 2, 3]
list2 = list1.copy()
list2.append(4)
print(list1) # Outputs [1, 2, 3]
What's Next?
Let's learn how to process list items cleanly using loops and shortcuts called list comprehensions.