List comprehensions
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Which list comprehension doubles every number in nums?
2. Which comprehension keeps only the marks that are 50 or more?
3. True or false: a list comprehension builds a NEW list and leaves the original list unchanged.
4. Which line is the correct list comprehension syntax?
5. Given names = ['ava', 'liam'], which comprehension makes ['AVA', 'LIAM']?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1[x * 2 for x in nums] | ABuilds a new list with every number in nums doubled | |
| 2[x for x in nums if x > 10] | BBuilds a new list with only the numbers in nums greater than 10 | |
| 3A list comprehension copies every item from a loop into a new list in one expression | CRound brackets make a generator, not a list. Square brackets are needed to build a list. | |
| 4A list comprehension can transform each item, for example by making each name uppercase | Dupper = [n.upper() for n in names] | |
| 5evens = [x for x in nums where x % 2 == 0] | Ecopy = [x for x in items] | |
| 6doubled = (x * 2 for x in nums) | F'where' is not Python. A condition in a list comprehension uses the keyword 'if'. |
C
Definitions
[x for x in items]
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
doubled = [x * 2 ___ x in nums]
2.
evens = [n for n in nums __ n % 2 == 0]
3.
squares = [_____ for n in range(1, 6)]
4.
marks = [55, 82, 47, 90]
passes = [m for m in marks if m __ 50]
5.
names = ["ava", "liam"]
big = [n._____() for n in names]
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
xs = [3, 8, 1, 9, 6]
B
# keep numbers bigger than 5
C
hi = [x for x xs if x > 5]
D
print(hi)
Question 2
A
prices = [5, 10, 20]
B
# double every price
C
dbl = (p * 2 for p in prices)
D
print(dbl)
Question 3
A
pets = ['cat', 'dog', 'emu']
B
up = [p.upper for p in pets]
C
print(up)
Question 4
A
nums = [1, 2, 3, 4]
B
sq = [n for n in nums]
C
print(sq)
Question 5
A
words = ['hi', 'yes', 'hello']
B
print('Lengths:')
C
# one length per word
D
lens = [len(w) for w in word]
E
print(lens)
Answer Key
List comprehensions
Section A: Quick Questions
Q1
B — [n * 2 for n in nums]
Q2
A — [m for m in marks if m >= 50]
Q3
B — True
Q4
A — squares = [x * x for x in items]
Q5
A — [n.upper() for n in names]
Section B: Match the Pairs
Q1
[x * 2 for x in nums] → Builds a new list with every number in nums doubled
Q2
[x for x in nums if x > 10] → Builds a new list with only the numbers in nums greater than 10
Q3
A list comprehension copies every item from a loop into a new list in one expression → copy = [x for x in items]
Q4
A list comprehension can transform each item, for example by making each name uppercase → upper = [n.upper() for n in names]
Q5
evens = [x for x in nums where x % 2 == 0] → 'where' is not Python. A condition in a list comprehension uses the keyword 'if'.
Q6
doubled = (x * 2 for x in nums) → Round brackets make a generator, not a list. Square brackets are needed to build a list.
Section C: Definitions
Q1
[x for x in items] — A list comprehension builds a new list from a loop in one expression. Add 'if condition' to filter items, or change x (e.g. x * 2) to transform each item.Section D: Fill in the Blanks
Q1
doubled = [x * 2 for x in nums]Q2
evens = [n for n in nums if n % 2 == 0]Q3
squares = [n * n for n in range(1, 6)]Q4
marks = [55, 82, 47, 90]
passes = [m for m in marks if m >= 50]Q5
names = ["ava", "liam"]
big = [n.upper() for n in names]Section E: Spot the Error
Q1
C — The keyword 'in' is missing. A list comprehension needs 'for x in xs' to loop over the list, so the line should be hi = [x for x in xs if x > 5].
Q2
C — Round brackets create a generator, not a list. A list comprehension uses square brackets: dbl = [p * 2 for p in prices].
Q3
B — upper is a method, so it needs brackets to be called. Without them the list holds method objects instead of uppercase text. It should be p.upper().
Q4
B — The expression at the front says how each item is transformed. Using just n copies the list unchanged. To square each item it should be n * n.
Q5
D — The list is called words, not word, so Python raises a NameError. The loop part must name the real list: for w in words.