List Comprehension Examples in Python for AP Computer Science

📚 Quick Study Guide

🔍 Definition: List comprehensions provide a concise way to create lists based on existing lists or iterables. 💡 Syntax: `[expression for item in iterable if condition]` (the `if` condition is optional). 📝 Expression: The expression that's evaluated for each item. 🧮 Iterable: The sequence (e.g., list, tuple, range) being iterated over. 📌 Condition: An optional filter that includes only items satisfying the condition. 💫 Benefit: Often more readable and faster than traditional `for` loops for creating lists. 🐍 Pythonic: List comprehensions are considered a very Pythonic way to write code.

🧪 Practice Quiz

1. What is the output of the following list comprehension? `[x2 for x in range(5)]` A. `[0, 1, 2, 3, 4]` B. `[1, 4, 9, 16, 25]` C. `[0, 1, 4, 9, 16]` D. `[0, 1, 4, 9, 16, 25]` 2. Which of the following list comprehensions correctly filters even numbers from a list? A. `[x for x in numbers if x % 2]` B. `[x for x in numbers if x % 2 == 0]` C. `[x if x % 2 == 0 for x in numbers]` D. `[x % 2 == 0 for x in numbers]` 3. What does this list comprehension do? `[c.upper() for c in "hello"]` A. Prints "hello" in uppercase. B. Returns a string "HELLO". C. Returns a list of uppercase characters: `['H', 'E', 'L', 'L', 'O']` D. Raises an error. 4. What is the value of `new_list` after running this code? python numbers = [1, 2, 3, 4, 5] new_list = [num * 2 for num in numbers if num > 2] A. `[2, 4, 6, 8, 10]` B. `[6, 8, 10]` C. `[3, 4, 5]` D. `[4, 6, 8]` 5. Which of the following is NOT a valid use case for list comprehensions? A. Creating a new list with modified elements from an existing list. B. Filtering elements from a list based on a condition. C. Performing complex calculations that require multiple nested loops. D. Creating a list of tuples from two different lists. 6. How can you create a list of the squares of odd numbers between 1 and 10 (inclusive) using list comprehension? A. `[x2 for x in range(1, 11) if x % 2 == 1]` B. `[x2 for x in range(1, 10) if x % 2 == 0]` C. `[x2 if x % 2 == 1 for x in range(1, 11)]` D. `[x**2 for x in range(1, 11)] if x % 2 == 1` 7. What will be the output of the following code? python matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] flattened = [num for row in matrix for num in row] print(flattened) A. `[[1, 2, 3], [4, 5, 6], [7, 8, 9]]` B. `[1, 2, 3, 4, 5, 6, 7, 8, 9]` C. `[3, 6, 9]` D. `[1, 4, 7]`

Click to see Answers

1. C
2. B
3. C
4. B
5. C
6. A
7. B