Python List Comprehension Multiple Choice Questions

📚 Quick Study Guide: Python List Comprehension

• 💡 What it is: List comprehension offers a concise way to create lists based on existing iterables (like other lists, tuples, strings, or ranges) in a single line of code. It's often more readable and efficient than traditional `for` loops.
• ✍️ Basic Syntax: The fundamental structure is [expression for item in iterable]. Here, the expression is evaluated for each item in the iterable, and the results form the new list.
• ✅ Conditional Logic (Filtering): You can add a condition to filter items using [expression for item in iterable if condition]. Only items for which the condition is true will be included in the new list.
• ⚖️ Conditional Logic (Transforming): For conditional transformations of items, you can use an if-else statement within the expression part: [expression_if_true if condition else expression_if_false for item in iterable].
• 🏗️ Nested List Comprehension: You can use multiple for clauses for creating lists from nested iterables, similar to nested loops: [expression for item1 in iterable1 for item2 in iterable2].
• ⚡ Benefits: Often leads to more compact and readable code, and can be significantly faster than explicit for loops for certain operations due to internal optimizations.
• 🧭 When to Use: Ideal for creating new lists by transforming or filtering elements from existing sequences. Avoid using it for complex logic that would make the single line unreadable.

📝 Practice Quiz

1. What is the output of the following code?
   numbers = [1, 2, 3, 4, 5]
squared_evens = [n*n for n in numbers if n % 2 == 0]
print(squared_evens)
   
   A. [1, 9, 25]
   B. [4, 16]
   C. [2, 4]
   D. [1, 4, 9, 16, 25]
2. Which of the following list comprehensions correctly generates a list of all uppercase letters from a given string `text = "Hello World"`?
   A. [char.upper() for char in text if char.islower()]
   B. [char for char in text if char.isupper()]
   C. [char for char in text if char.is_upper()]
   D. [char for char in text if char.upper()]
3. Consider the code:
   words = ["apple", "banana", "cherry"]
lengths = [len(word) for word in words]
print(lengths)
   What will be printed to the console?
   A. [5, 6, 6]
   B. [5, 6, 7]
   C. ["apple", "banana", "cherry"]
   D. [len(word), len(word), len(word)]
4. What is the output of this list comprehension?
   matrix = [[1, 2], [3, 4], [5, 6]]
flattened = [num for row in matrix for num in row]
print(flattened)
   
   A. [[1, 2], [3, 4], [5, 6]]
   B. [1, 2, 3, 4, 5, 6]
   C. [1, 3, 5, 2, 4, 6]
   D. [[1, 3, 5], [2, 4, 6]]
5. Which list comprehension will create a list of numbers from 0 to 9, where even numbers are replaced by the string "Even" and odd numbers remain as they are?
   A. ["Even" if x % 2 == 0 for x in range(10) else x]
   B. [x if x % 2 != 0 else "Even" for x in range(10)]
   C. [x if x % 2 == 0 else "Even" for x in range(10)]
   D. ["Even" for x in range(10) if x % 2 == 0 else x]
6. Given data = [10, -5, 20, -15, 0], what will be the result of:
   positive_numbers = [x for x in data if x > 0]
print(positive_numbers)
   
   A. [10, 20, 0]
   B. [10, 20]
   C. [-5, -15]
   D. [10, -5, 20, -15, 0]
7. What is the most Pythonic way to create a list of tuples, where each tuple contains a number and its cube for numbers from 1 to 3?
   A. my_list = []
for i in range(1, 4):
my_list.append((i, i3))
   B. [(i, i3) for i in range(1, 4)]
   C. list(map(lambda i: (i, i3), range(1, 4)))
   D. generate_tuples = lambda i: (i, i3)
my_list = [generate_tuples(i) for i in range(1, 4)]