6.3a Lists in Python — Edexcel 1CP2

What is a List?

A list in Python is an ordered, mutable (changeable) collection of items. Items can be of different data types. Lists are defined using square brackets [] and items are separated by commas.

# Creating lists
numbers = [10, 20, 30, 40, 50]
names = ["Alice", "Bob", "Charlie"]
mixed = [42, "hello", True, 3.14]   # different types
empty = []                                 # empty list

Accessing Items

Items are accessed using their index (starting at 0). Negative indices count from the end.

colours = ["red", "green", "blue", "yellow"]
print(colours[0])   # "red"
print(colours[2])   # "blue"
print(colours[-1])  # "yellow" (last item)
print(colours[-2])  # "blue" (second from last)

List Methods

Method	What it does	Example
`.append(x)`	Adds x to the END of the list	`nums.append(6)`
`.insert(i, x)`	Inserts x at position i	`nums.insert(0, 99)`
`.remove(x)`	Removes first occurrence of x	`nums.remove(20)`
`.pop()`	Removes and returns last item	`last = nums.pop()`
`.sort()`	Sorts list in ascending order (in place)	`nums.sort()`
`.reverse()`	Reverses list in place	`nums.reverse()`
`.index(x)`	Returns index of first occurrence of x	`nums.index(30)`
`len(list)`	Returns number of items	`len(nums)`

scores = [85, 72, 91, 64]
scores.append(78)      # [85, 72, 91, 64, 78]
scores.sort()          # [64, 72, 78, 85, 91]
print(scores[0])      # 64 — lowest score
print(scores[-1])     # 91 — highest score
print(len(scores))    # 5

Iterating Over Lists

A for loop is ideal for processing every item in a list:

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

for fruit in fruits:
    print(fruit)          # prints each fruit

# Using index with range
for i in range(len(fruits)):
    print(i, fruits[i])   # 0 apple, 1 banana, 2 cherry

Searching Lists

nums = [10, 20, 30, 40]

if 20 in nums:
    print("Found!")         # use 'in' to test membership

# Linear search — find position manually
target = 30
for i in range(len(nums)):
    if nums[i] == target:
        print("Found at index", i)

2D Lists (Nested Lists)

A list can contain other lists — useful for grids, tables, or matrices:

grid = [[1, 2, 3],
        [4, 5, 6],
        [7, 8, 9]]

print(grid[0][0])   # 1 — row 0, column 0
print(grid[1][2])   # 6 — row 1, column 2
print(grid[2][1])   # 8 — row 2, column 1

Exam tip: Lists are the Python equivalent of arrays in Edexcel pseudocode. Common exam tasks include: finding the maximum/minimum value, counting occurrences, searching for an item, and calculating totals/averages. Always practise writing loops over lists.

⚠️ Common Mistakes

Index out of range error — if a list has 5 items, valid indices are 0–4 (NOT 5)
Confusing .append() (adds one item to end) with .insert() (adds at specific position)
Forgetting .sort() modifies the list IN PLACE — it does not return a new sorted list
Modifying a list while iterating over it can cause unexpected behaviour
2D list indexing is grid[row][column] — row first, then column

▶

Video coming soon

Click slide or press arrow keys to navigate

✍️

Worksheet — 6.3a Lists in Python

8 Edexcel-style questions · instantly marked

Q1Given: items = ["pen", "book", "ruler", "eraser"]. What is the output of print(items[2]) and print(items[-1])?[2]

✅ Mark scheme

items[2] = "ruler" [1]; items[-1] = "eraser" [1]. Index 2 is the third item (0-indexed). Negative index -1 is always the last item.

Q2Write Python code to create an empty list called 'students', then add three names to it using .append().[4]

✅ Mark scheme

students = [] [1]; students.append("Alice") [1]; students.append("Bob") [1]; students.append("Charlie") [1]. (Accept any valid names. .append() adds to the end of the list each time.)

Q3Write a for loop to print every item in: colours = ["red", "green", "blue", "yellow"][2]

✅ Mark scheme

for colour in colours: [1]; print(colour) [1] — indented under the for loop. (Accept: for c in colours / for i in range(len(colours)): print(colours[i]) — any valid loop.)

Q4What is the difference between .append() and .insert() in Python lists?[2]

✅ Mark scheme

.append(x) adds item x to the END of the list [1]; .insert(i, x) inserts item x at a specified index i, shifting existing items right [1]. Example: list.insert(0, "x") adds "x" to the front.

Q5Write Python code that: creates a list of 5 numbers, then calculates and prints the total (sum) and average.[5]

✅ Mark scheme

nums = [10, 20, 30, 40, 50] or any 5 numbers [1]; total = 0 [1]; for n in nums: total += n [1]; print(total) [1]; print(total / len(nums)) [1]. (Accept: using sum() built-in: total = sum(nums), average = total/len(nums).)

Q6What does the following code output? grid = [[1,2],[3,4],[5,6]]; print(grid[1][0])[2]

✅ Mark scheme

3 [2]. grid[1] accesses the second sub-list [3,4] [1 for understanding]; [0] then gets the first element = 3 [1]. 2D list is indexed [row][column].

Q7Write a program that asks the user for 5 numbers (one at a time), stores them in a list, sorts the list, then prints it.[5]

✅ Mark scheme

nums = [] [1]; for i in range(5): [1]; n = int(input("Enter a number: ")) [1]; nums.append(n) [1]; nums.sort() [1]; print(nums). (Must use int() to convert input since input() returns a string.)

Q8Write a linear search function that takes a list and a target value as parameters, and returns the index if found or -1 if not found.[4]

✅ Mark scheme

def linear_search(lst, target): [1]; for i in range(len(lst)): [1]; if lst[i] == target: return i [1]; return -1 [1]. The return -1 must be OUTSIDE the loop (correct indentation critical). -1 is a conventional way to signal "not found".

Topic Quiz

Q 1 of 15

You scored

out of 15

Click to reveal definition

🎉

Session complete!

Term	Definition

🔒

Unlock Pro

Subscribe to access all 59 Edexcel 1CP2 lessons.

£7.99/month

or £59/year

What is a List?

Accessing Items

List Methods

Iterating Over Lists

Searching Lists

2D Lists (Nested Lists)

Worksheet — 6.3a Lists in Python

Mini Test — Lists in Python

Unlock Pro