Lesson 32: List Methods - Python Course

Introduction to List Methods

List methods are built-in functions that allow you to manipulate lists efficiently. These methods provide powerful ways to add, remove, modify, and organize items in your lists. Understanding list methods is essential for working effectively with lists in Python.

Methods are called using dot notation: list_name.method(). Most list methods modify the list in place, meaning they change the original list rather than creating a new one.

Adding Items

Several methods allow you to add items to a list:

adding_items.py
# append() - adds item to the end
fruits = ["apple", "banana"]
fruits.append("cherry")
print(fruits)  # ['apple', 'banana', 'cherry']

# insert() - adds item at specific position
fruits.insert(1, "orange")
print(fruits)  # ['apple', 'orange', 'banana', 'cherry']

# extend() - adds multiple items from another list
more_fruits = ["grape", "mango"]
fruits.extend(more_fruits)
print(fruits)  # ['apple', 'orange', 'banana', 'cherry', 'grape', 'mango']

# You can also use += operator
fruits += ["kiwi"]
print(fruits)

Removing Items

Methods for removing items from lists:

removing_items.py
# remove() - removes first occurrence of value
fruits = ["apple", "banana", "cherry", "banana"]
fruits.remove("banana")
print(fruits)  # ['apple', 'cherry', 'banana']

# pop() - removes and returns item at index (default: last item)
last = fruits.pop()
print(last)     # 'banana'
print(fruits)   # ['apple', 'cherry']

first = fruits.pop(0)
print(first)    # 'apple'
print(fruits)   # ['cherry']

# clear() - removes all items
fruits.clear()
print(fruits)  # []

Finding and Counting

Methods to search and count items in lists:

finding_items.py
# index() - returns index of first occurrence
fruits = ["apple", "banana", "cherry"]
idx = fruits.index("banana")
print(idx)  # 1

# count() - counts occurrences of value
numbers = [1, 2, 2, 3, 2]
print(numbers.count(2))  # 3

# Check if item exists before using index()
if "orange" in fruits:
    idx = fruits.index("orange")
    print(f"Found at index {idx}")

Sorting and Reversing

Methods to organize list items:

sorting.py
# sort() - sorts list in place (ascending by default)
numbers = [3, 1, 4, 1, 5]
numbers.sort()
print(numbers)  # [1, 1, 3, 4, 5]

# Sort in descending order
numbers.sort(reverse=True)
print(numbers)  # [5, 4, 3, 1, 1]

# reverse() - reverses order of items
fruits = ["apple", "banana", "cherry"]
fruits.reverse()
print(fruits)  # ['cherry', 'banana', 'apple']

# Note: sorted() is a function that returns new list
original = [3, 1, 2]
new_list = sorted(original)
print(original)  # [3, 1, 2] (unchanged)
print(new_list)  # [1, 2, 3] (sorted)

Copying Lists

Methods to create copies of lists:

copying.py
# copy() - creates shallow copy
original = [1, 2, 3]
new_list = original.copy()
new_list.append(4)
print(original)  # [1, 2, 3] (unchanged)
print(new_list)   # [1, 2, 3, 4]

# Slicing also creates a copy
another_copy = original[:]
another_copy.append(5)
print(original)     # [1, 2, 3]
print(another_copy) # [1, 2, 3, 5]

# Be careful: assignment creates reference, not copy
reference = original
reference.append(6)
print(original)  # [1, 2, 3, 6] (changed!)
print(reference) # [1, 2, 3, 6]

Common List Methods Summary

append(item) - Add item to end
insert(index, item) - Insert item at position
extend(iterable) - Add multiple items
remove(item) - Remove first occurrence
pop([index]) - Remove and return item
clear() - Remove all items
index(item) - Find index of item
count(item) - Count occurrences
sort([reverse]) - Sort in place
reverse() - Reverse order
copy() - Create shallow copy

Best Practices

✅ Method Usage Tips

• Most list methods modify the list in place (they don't return a new list)

• Use copy() when you need to modify a list without changing the original

• pop() is useful when you need both the item and its removal

• Check if item exists before using index() to avoid errors

• sort() modifies the original; use sorted() if you need the original unchanged

List Methods