How to Use Python Lists (list)

Creating a list

With a list (list), you can hold several values together in one place. Unlike int or str, where a variable holds a single value, a list can line up any number of values side by side.

You declare one by wrapping values in [ and ], separated by commas.

Just like with strings, you access items by 0-based index. [0] gives you the first, and [-1] gives you the last.

A key feature of lists is that you can change the values afterward.

# Declaring a list
numbers = [10, 20, 30, 40]

# Empty list (to be filled in later)
empty = []

# Access
print(numbers[0])     # 10
print(numbers[-1])    # 40

# Overwrite
numbers[1] = 99
print(numbers)        # [10, 99, 30, 40]

# Mixed types are fine
mixed = [1, "apple", 3.14, True]
print(mixed[1])       # apple

Nested lists (lists inside lists)

You can also put lists inside a list, like [[1, 2], [3, 4]]. To pull a value out, you chain two indices as in data[1][0]. It's handy for table-shaped data, but a plain flat list is plenty while you're getting started.

Let's work with a shopping list of fruits.

① Create fruits = ["apple", "banana", "grape", "lemon"], then print() the first and last items.

② Replace fruits[1] with "orange" and print() the whole list.

Slicing

Lists use the same slice syntax as strings. [start:end] gives a sub-list, [::step] steps through the list, and [-n:] grabs the last n items.

The result of a slice is a list.

nums = [1, 2, 3, 4, 5]

print(nums[:3])    # [1, 2, 3]
print(nums[2:])    # [3, 4, 5]
print(nums[-2:])   # [4, 5]
print(nums[::2])   # [1, 3, 5] (every other one)

# The original list doesn't change (a new list is returned)
print(nums)        # [1, 2, 3, 4, 5]

You're given scores = [72, 85, 91, 68, 77, 95].

① Use a slice to pull out the first 3 ([72, 85, 91]) and print them.

② Use a slice to pull out the last 2 ([77, 95]) and print them.

Adding and removing items

Lists come with plenty of methods to add or remove items. These methods change the list itself. In other words, calling list.append(...) modifies list in place.

box = [1, 2, 3]

# Add
box.append("apple")       # add one to the end
print(box)                # [1, 2, 3, 'apple']

box.extend(["banana", "grape"])  # unpack and append at the end
print(box)                # [1, 2, 3, 'apple', 'banana', 'grape']

box.insert(1, "NEW")      # insert at index 1
print(box)                # [1, 'NEW', 2, 3, 'apple', 'banana', 'grape']

# Remove
box.remove("apple")       # remove the first match by value
print(box)                # [1, 'NEW', 2, 3, 'banana', 'grape']

v = box.pop(0)            # take out index 0 and return it
print(v)                  # 1
print(box)                # ['NEW', 2, 3, 'banana', 'grape']

remove / pop on something that's not there → error

remove(x) raises ValueError if x isn't in the list, and pop(i) raises IndexError if i is out of range. A safe pattern is to check for presence first with if x in box: before removing.

Let's edit a To-Do list.

You start with todo = ["shopping", "gym"].

① Use append to add "reading" to the end.

② Use extend to add ["walk", "study"] to the end all at once.

③ Use insert to drop "breakfast" at the front.

④ Use remove to delete "gym", then print() the final list.

Sorting and searching (sort / reverse / count / index)

Lists also have sorting and searching methods. The important thing here is that there are two kinds of methods.

- Methods that modify the list (sort / reverse) → don't capture a return value; the list itself changes

- Methods that return a value (count / index) → use the return value, as in print(list.count(...))

fruits = ["banana", "lemon", "apple", "grape"]

# (1) Modifying methods: the list changes just by calling them
fruits.sort()
print(fruits)          # ['apple', 'banana', 'grape', 'lemon']

fruits.reverse()
print(fruits)          # ['lemon', 'grape', 'banana', 'apple']

# (2) Returning methods: capture and use the return value
nums = [1, 2, 2, 3, 2, 4]
print(nums.count(2))   # 3 (there are three 2s)
print(nums.index(3))   # 3 (3 is the 4th item = index 3)

Why print(fruits.sort()) prints None

A common mistake: writing print(fruits.sort()) and seeing None printed. sort() doesn't return a value — it sorts fruits in place.

The right fix is to call fruits.sort() on its own, then print(fruits) on the next line — split it into two lines.

By the way, the details of return values (the values that methods and functions hand back) will be covered in the articles on functions and object-oriented programming. For now, it's enough to remember the two patterns: "sort / reverse change the list just by being called" and "count / index are captured with = and then used".

Let's analyze a list of test scores: scores = [72, 85, 91, 68, 77, 95, 85].

① Use sort() to sort ascending, then print() the sorted list.

② Use count() to print() how many people scored 85.

In this article, we covered creating and accessing lists, slicing, adding and removing items, and sorting and searching.