Runtime error: index out of range
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. A list has 5 items: scores = [4, 8, 6, 9, 7]. Which statement is true about scores[5]?
2. Which expression gives the last valid index of a list called items?
3. Which loop header causes an off-by-one IndexError when reading names[i]?
4. Given names = [], what happens when the code runs print(names[0])?
5. Which check helps prevent an IndexError before using items[i]?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1items[len(items)] | Aif 0 <= i < len(items): print(items[i]) | |
| 2items[len(items) - 1] | Bitems = [] print(items[0]) | |
| 3Prevent an IndexError with a range check before using the index | CGets the last item in the list safely, as long as the list is not empty | |
| 4Accessing the first item of an empty list causes an IndexError | DRaises an IndexError, because the last valid index is len(items) - 1 | |
| 5for i in range(len(items) + 1): print(items[i]) | EA 3-item list only has indexes 0, 1 and 2, so index 3 is out of range. The last item is scores[2] or scores[-1]. | |
| 6scores = [70, 85, 90] print(scores[3]) | FOff-by-one error: the loop goes one step too far, so the last value of i equals len(items) and raises an IndexError. Use range(len(items)). |
C
Definitions
IndexError
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
items = [4, 8, 15, 16, 23]
last = items[len(items) - _]
print(last)
2.
items = ["a", "b", "c"]
for i in range(___(items)):
print(items[i])
3.
items = []
if len(items) _ 0:
print(items[0])
4.
try:
print(items[5])
except __________:
5.
if index >= 0 and index _ len(items):
print(items[index])
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
scores = [4, 8, 6, 9, 7]
B
last = len(scores) - 1
C
print(scores[last + 1])
Question 2
A
names = ['Ava', 'Zoe', 'Leo']
B
count = len(names)
C
print('Names:', count)
D
for i in range(count + 1):
E
print(names[i])
Question 3
A
items = [10, 20, 30, 40]
B
total = 0
C
i = 0
D
while i <= len(items):
E
total += items[i]
F
i += 1
Question 4
A
prices = [3, 5, 8]
B
last = prices[len(prices)]
C
print(last)
Question 5
A
colours = ['red']
B
print(colours[0])
C
print(colours[1])
Answer Key
Runtime error: index out of range
Section A: Quick Questions
Q1
A — It raises an IndexError because the last valid index is 4
Q2
A — len(items) - 1
Q3
A — for i in range(len(names) + 1):
Q4
B — An IndexError is raised because an empty list has no index 0
Q5
B — if i >= 0 and i < len(items):
Section B: Match the Pairs
Q1
items[len(items)] → Raises an IndexError, because the last valid index is len(items) - 1
Q2
items[len(items) - 1] → Gets the last item in the list safely, as long as the list is not empty
Q3
Prevent an IndexError with a range check before using the index → if 0 <= i < len(items):
print(items[i])
Q4
Accessing the first item of an empty list causes an IndexError → items = []
print(items[0])
Q5
for i in range(len(items) + 1):
print(items[i]) → Off-by-one error: the loop goes one step too far, so the last value of i equals len(items) and raises an IndexError. Use range(len(items)).
Q6
scores = [70, 85, 90]
print(scores[3]) → A 3-item list only has indexes 0, 1 and 2, so index 3 is out of range. The last item is scores[2] or scores[-1].
Section C: Definitions
Q1
IndexError — A runtime error raised when code uses an index that is not in the list, such as items[5] in a 5-item list. The last valid index is len(items) - 1.Section D: Fill in the Blanks
Q1
items = [4, 8, 15, 16, 23]
last = items[len(items) - 1]
print(last)Q2
items = ["a", "b", "c"]
for i in range(len(items)):
print(items[i])Q3
items = []
if len(items) > 0:
print(items[0])Q4
try:
print(items[5])
except IndexError:Q5
if index >= 0 and index < len(items):
print(items[index])Section E: Spot the Error
Q1
C — The list has 5 items, so the last valid index is 4 (len(scores) - 1). Using last + 1 gives index 5, which raises an IndexError. It should be print(scores[last]).
Q2
D — This is an off-by-one error. range(count + 1) makes i reach 3, but the valid indexes are 0 to 2, so names[3] raises an IndexError. It should be range(count).
Q3
D — With <=, the loop runs when i equals 4, but the last valid index is 3. items[4] raises an IndexError. The condition should be i < len(items).
Q4
B — len(prices) is 3, but indexes only go up to 2. The last item is at len(prices) - 1. Without the - 1, the code raises an IndexError.
Q5
A — With only one item, the only valid index is 0. Then colours[1] on line 3 raises an IndexError. The list needs two items, 'red' and 'blue'.