Online Learning Platform
Python List Practice Problems
Write a Python program to print the squares of all even numbers in a list.
[1, 2, 3, 4, 5, 6]
[4, 16, 36]
numbers = [1, 2, 3, 4, 5, 6]print([n * n for n in numbers if n % 2 == 0])[4, 16, 36]
New to this topic? Read the lesson, then come back.
Write a Python program to print every pair of elements from a list whose sum is 10.
[2, 8, 5, 3, 7, 5, 1]
[(2, 8), (5, 5), (3, 7)]
numbers = [2, 8, 5, 3, 7, 5, 1]pairs = []for i in range(len(numbers)): for j in range(i + 1, len(numbers)): if numbers[i] + numbers[j] == 10: pairs.append((numbers[i], numbers[j]))print(pairs)[(2, 8), (5, 5), (3, 7)]
Starting the inner loop at i + 1 avoids pairing an item with itself or counting a pair twice.
New to this topic? Read the lesson, then come back.
Write a Python program to remove every duplicate value from a list, keeping the first occurrence of each value in its original position.
[5, 7, 8, 2, 5, 0, 7, 2]
[5, 7, 8, 2, 0]
list1 = [5, 7, 8, 2, 5, 0, 7, 2]result = [] for value in list1: if value not in result: result.append(value) print(result)[5, 7, 8, 2, 0]
The input list; 5, 7 and 2 each appear twice.
result starts empty and collects each value once.
The loop reads the values left to right, so the first occurrence is always seen first.
value not in result is True only the first time a value appears.
append() adds that first occurrence to the end of result.
list1 = [5, 7, 8, 2, 5, 0, 7, 2]result = list(dict.fromkeys(list1))print(result)[5, 7, 8, 2, 0]
Dictionary keys are unique and remember insertion order, so this drops repeats and keeps the first position of each value.
list(set(list1)) also removes duplicates, but a set does not keep the original order, so it is not a correct answer when order matters.
The loop is easy to follow but checks in result for every item (O(n²)); dict.fromkeys() runs in O(n) and is what you should use in real code.
New to this topic? Read the lesson, then come back.
Write a Python program to separate the even and odd numbers of a list.
[5, 8, 3, 12, 7, 10]
Even: [8, 12, 10] Odd: [5, 3, 7]
numbers = [5, 8, 3, 12, 7, 10]evens = [n for n in numbers if n % 2 == 0]odds = [n for n in numbers if n % 2 != 0]print("Even:", evens)print("Odd:", odds)Even: [8, 12, 10] Odd: [5, 3, 7]
New to this topic? Read the lesson, then come back.
Write a Python program to find the smallest and largest elements of a list.
[45, 12, 89, 3, 67]
Min: 3 Max: 89 3 89
min() and max().numbers = [45, 12, 89, 3, 67]smallest = largest = numbers[0]for n in numbers: if n < smallest: smallest = n if n > largest: largest = nprint("Min:", smallest, "Max:", largest)print(min(numbers), max(numbers))Min: 3 Max: 89 3 89
Both start at the first item, which works for negative numbers too.
New to this topic? Read the lesson, then come back.
Write a Python program to find the product of all elements in a list.
[2, 3, 4, 5]
120 120
math.prod().import math numbers = [2, 3, 4, 5]product = 1for n in numbers: product *= nprint(product, math.prod(numbers))120 120
Starting at 1 (not 0) keeps the product correct.
New to this topic? Read the lesson, then come back.
Write a Python program to calculate the sum of all elements in a list.
[12, 7, 33, 5, 21]
78 78
sum().numbers = [12, 7, 33, 5, 21]total = 0for n in numbers: total += nprint(total, sum(numbers))78 78
The loop adds each number to the running total.
The built-in sum() gives the same answer.
New to this topic? Read the lesson, then come back.
Write a Python program to combine two lists.
[1, 2, 3], [4, 5, 6]
[1, 2, 3, 4, 5, 6] [1, 2, 3, 4, 5, 6]
+ creates a new list; extend() adds to an existing one.list1 = [1, 2, 3]list2 = [4, 5, 6]print(list1 + list2)list1.extend(list2)print(list1)[1, 2, 3, 4, 5, 6] [1, 2, 3, 4, 5, 6]
+ returns a new list and leaves both originals unchanged.
extend changes list1 in place.
New to this topic? Read the lesson, then come back.
Write a Python program to calculate the square of each number in a list.
[2, 4, 6, 8, 10]
[4, 16, 36, 64, 100]
numbers = [2, 4, 6, 8, 10]squares = []for n in numbers: squares.append(n ** 2)print(squares)[4, 16, 36, 64, 100]
Start with an empty list for the results.
n ** 2 squares each number and append adds it to the end.
numbers = [2, 4, 6, 8, 10]print([n ** 2 for n in numbers])[4, 16, 36, 64, 100]
The comprehension does the same loop in one expression.
New to this topic? Read the lesson, then come back.
100 list programs, from sums and reversing to sublists, de-duplication and run-length decoding. Lists are Python’s most used data structure, and these exercises appear in most Python interviews. Every solution is explained and shows its real output.
Read the Lists and List Comprehension lesson first if the topic is new to you.
reversed() and with reverse().Easyextend().Easysort() and with sorted().Easypop().Easy