Chapter 5: Data Structures

50 Find the Bug exercises from Chapter 5 of Everyday Programming. Every program below is short, does something recognizable, and hides exactly one bug — syntax, runtime, or logical. Read it, predict what it does, then run it and find out.

Worked solutions for this chapter: Chapter 5 solutions. Every snippet is also available as a .py file — see Exercises & Solutions.

int

Exercise 5.1.1 — Total points

A quiz has 3 sections worth 20, 30, and 25 points. The program should print the total, 75.

section1 = 20
section2 = 30
section3 = 25

total = section1 + section2 - section3
print(total)   # 75

Solution 5.1.1 · ex_5_1_1.py

Exercise 5.1.2 — Students per team

Thirty students are split evenly into 5 teams. The program should print the whole number 6.

students = 30
teams = 5

per_team = students / teams
print(per_team)   # 6

Solution 5.1.2 · ex_5_1_2.py

Exercise 5.1.3 — Seconds in an hour

There are 60 seconds in a minute and 60 minutes in an hour. The program should print 3600.

seconds_per_minute = 60
minutes_per_hour = 60

seconds_per_hour = seconds_per_minute + minutes_per_hour
print(seconds_per_hour)   # 3600

Solution 5.1.3 · ex_5_1_3.py

Exercise 5.1.4 — Counting by tens

The program should add 10 to a starting count and print 110.

count = 100
count = count + "10"
print(count)   # 110

Solution 5.1.4 · ex_5_1_4.py

Exercise 5.1.5 — Apples per box

You have 17 apples and want 5 per box. The program should print how many full boxes (3) you can fill.

apples = 17
per_box = 5

full_boxes = apples % per_box
print(full_boxes)   # 3

Solution 5.1.5 · ex_5_1_5.py

float

Exercise 5.2.1 — Average temperature

Three readings are 20.0, 22.0, and 24.0 degrees. The program should print the average, 22.0.

reading1 = 20.0
reading2 = 22.0
reading3 = 24.0

average = reading1 + reading2 + reading3 / 3
print(average)   # 22.0

Solution 5.2.1 · ex_5_2_1.py

Exercise 5.2.2 — Splitting a bill

A 50-dollar bill is split between 4 people. The program should print 12.5.

bill = 50
people = 4

each = bill // people
print(each)   # 12.5

Solution 5.2.2 · ex_5_2_2.py

Exercise 5.2.3 — Rounding a price

A price of 3.14159 dollars should be rounded to 2 decimal places, printing 3.14.

price = 3.14159
rounded = round(price)
print(rounded)   # 3.14

Solution 5.2.3 · ex_5_2_3.py

Exercise 5.2.4 — Half of a measurement

A board is 9.0 meters long. The program should print half its length, 4.5.

length = 9.0
half = length / 2
print(half   # 4.5

Solution 5.2.4 · ex_5_2_4.py

Exercise 5.2.5 — Celsius to Fahrenheit

The program converts 100.0 degrees Celsius to Fahrenheit and should print 212.0.

celsius = 100.0
fahrenheit = celsius * 9 / 5 - 32
print(fahrenheit)   # 212.0

Solution 5.2.5 · ex_5_2_5.py

bool

Exercise 5.3.1 — Is it freezing?

Water freezes at 0 degrees Celsius. The program should report True when the temperature is below freezing. With temp = -5 it should print True.

temp = -5
is_freezing = temp > 0
print(is_freezing)   # True

Solution 5.3.1 · ex_5_3_1.py

Exercise 5.3.2 — Passing grade

A grade of 60 or more passes. With a grade of 72, the program should print True.

grade = 72
passed = grade >= 60
print(Passed)   # True

Solution 5.3.2 · ex_5_3_2.py

Exercise 5.3.3 — Both lights on

A room is “ready” only if both lights are on. The program should print False here, since one light is off.

light1_on = True
light2_on = False

ready = light1_on or light2_on
print(ready)   # False

Solution 5.3.3 · ex_5_3_3.py

Exercise 5.3.4 — Empty cart

A cart is empty when it has 0 items. The program should print True.

items = 0
is_empty = items = 0
print(is_empty)   # True

Solution 5.3.4 · ex_5_3_4.py

Exercise 5.3.5 — Within speed limit

The limit is 65. A car going 60 is within the limit, so the program should print True.

speed = 60
limit = 65

within_limit = speed > limit
print(within_limit)   # True

Solution 5.3.5 · ex_5_3_5.py

Strings

Exercise 5.4.1 — First letter

The program should print the first letter of a city name: T.

city = "Tokyo"
first = city[1]
print(first)   # T

Solution 5.4.1 · ex_5_4_1.py

Exercise 5.4.2 — Shouting

The program should print a greeting in all capitals: HELLO.

word = "hello"
loud = word.upper
print(loud)   # HELLO

Solution 5.4.2 · ex_5_4_2.py

Exercise 5.4.3 — Full name

The program should join a first and last name with a space: “Maya Singh”.

first = "Maya"
last = "Singh"

full = first + last
print(full)   # Maya Singh

Solution 5.4.3 · ex_5_4_3.py

Exercise 5.4.4 — Length of a word

The program should print the number of letters in “science”: 7.

word = "science"
count = len(word())
print(count)   # 7

Solution 5.4.4 · ex_5_4_4.py

Exercise 5.4.5 — Last three characters

The program should print the last three characters of a code: “789”.

code = "ABC789"
last_three = code[-3]
print(last_three)   # 789

Solution 5.4.5 · ex_5_4_5.py

None

Exercise 5.5.1 — No reading yet

A sensor has no reading. The program should print True because the reading is None.

reading = None
no_data = reading == "None"
print(no_data)   # True

Solution 5.5.1 · ex_5_5_1.py

Exercise 5.5.2 — Default color

The function should return a default color when none is given. Calling it with nothing should print “blue”.

def choose_color(color):
    if color is None:
        color = "blue"

print(choose_color(None))   # blue

Solution 5.5.2 · ex_5_5_2.py

Exercise 5.5.3 — Checking for a value

When a value is None, the program should print “missing”.

favorite = None

if favorite is not None:
    print("missing")
else:
    print("has value")
# expected: missing

Solution 5.5.3 · ex_5_5_3.py

Exercise 5.5.4 — Length of nothing

A list of temperatures has not been filled in yet, so it is None. The program tries to count it and should instead detect the missing list and print 0.

temps = None
count = len(temps)
print(count)   # 0

Solution 5.5.4 · ex_5_5_4.py

Exercise 5.5.5 — Comparing to None

The program should check whether a username has been set, printing True when it is still None.

username = None
not_set = username is None
print(Not_set)   # True

Solution 5.5.5 · ex_5_5_5.py

Lists

Exercise 5.6.1 — First fruit

The program should print the first fruit in the list: “apple”.

fruits = ["apple", "banana", "orange"]
print(fruits[1])   # apple

Solution 5.6.1 · ex_5_6_1.py

Exercise 5.6.2 — Adding an item

The program should add “grape” to the list and print 4 items in total.

fruits = ["apple", "banana", "orange"]
fruits.add("grape")
print(len(fruits))   # 4

Solution 5.6.2 · ex_5_6_2.py

Exercise 5.6.3 — Last score

The program should print the last score in the list: 88.

scores = [70, 95, 88]
print(scores[3])   # 88

Solution 5.6.3 · ex_5_6_3.py

Exercise 5.6.4 — Changing a value

The program should change the second price to 5.0 and print the list.

prices = [2.0, 3.0, 4.0]
prices(1) = 5.0
print(prices)   # [2.0, 5.0, 4.0]

Solution 5.6.4 · ex_5_6_4.py

Exercise 5.6.5 — How many items

The program should print how many items are in the shopping list: 3.

shopping = ["milk", "eggs", "bread"]
count = len(shopping) - 1
print(count)   # 3

Solution 5.6.5 · ex_5_6_5.py

Tuples

Exercise 5.7.1 — Map coordinates

A location is stored as a (latitude, longitude) tuple. The program should print the latitude, 41.8781.

location = (41.8781, -87.6298)
print(location[1])   # 41.8781

Solution 5.7.1 · ex_5_7_1.py

Exercise 5.7.2 — A fixed pair

This program should change the width to 1280 and print (1280, 1080).

size = (1920, 1080)
size[0] = 1280
print(size)   # expected: (1280, 1080)

Solution 5.7.2 · ex_5_7_2.py

Exercise 5.7.3 — Unpacking coordinates

The program should unpack a tuple into two variables and print “lat 35.7, lon 139.7”.

coords = (35.7, 139.7)
lat = coords
lon = coords
print(f"lat {lat}, lon {lon}")   # lat 35.7, lon 139.7

Solution 5.7.3 · ex_5_7_3.py

Exercise 5.7.4 — A single value

The program should make a one-element tuple holding the number 42 and print its length, 1.

single = (42)
print(len(single))   # 1

Solution 5.7.4 · ex_5_7_4.py

Exercise 5.7.5 — Days in a tuple

A tuple holds three weekday names. The program should print the second one, “Tue”.

days = ("Mon", "Tue", "Wed")
print(days[2])   # Tue

Solution 5.7.5 · ex_5_7_5.py

Sets

Exercise 5.8.1 — Unique colors

A set removes duplicates. The program should print how many unique colors there are: 3.

colors = ["red", "blue", "red", "green"]
print(len(colors))   # 3

Solution 5.8.1 · ex_5_8_1.py

Exercise 5.8.2 — Adding a member

The program should add “Sydney” to the set of cities and print 4 members in total.

cities = {"New York", "London", "Tokyo"}
cities.append("Sydney")
print(len(cities))   # 4

Solution 5.8.2 · ex_5_8_2.py

Exercise 5.8.3 — Is it a member?

The program should check whether “blue” is in the set and print True.

colors = {"red", "blue", "green"}
print("yellow" in colors)   # True

Solution 5.8.3 · ex_5_8_3.py

Exercise 5.8.4 — Shared subjects

Two students list their subjects. The program should print the subjects they share: {“math”}.

maya = {"math", "science", "art"}
leo = {"math", "history"}

shared = maya | leo
print(shared)   # {'math'}

Solution 5.8.4 · ex_5_8_4.py

Exercise 5.8.5 — Building a set

The program should start with an empty set, add one item, and print the set with that item.

seen = {}
seen.add("apple")
print(seen)   # {'apple'}

Solution 5.8.5 · ex_5_8_5.py

Dictionaries

Exercise 5.9.1 — Looking up a name

A student record stores a name. The program should print “Maya”.

student = {"name": "Maya", "grade": 10}
print(student["Name"])   # Maya

Solution 5.9.1 · ex_5_9_1.py

Exercise 5.9.2 — Updating a grade

The program should change the grade to 11 and print 11.

student = {"name": "Maya", "grade": 10}
student("grade") = 11
print(student["grade"])   # 11

Solution 5.9.2 · ex_5_9_2.py

Exercise 5.9.3 — Missing key

The program should safely look up a missing subject and print “not found” instead of crashing.

student = {"name": "Maya", "grade": 10}
subject = student["favorite_subject"]
print(subject)   # not found

Solution 5.9.3 · ex_5_9_3.py

Exercise 5.9.4 — Safe default with get

Using .get, the program should print “science” when the key exists.

student = {"favorite_subject": "science"}
subject = student.get("favorite_subject", "unknown")
print(Subject)   # science

Solution 5.9.4 · ex_5_9_4.py

Exercise 5.9.5 — Adding an entry

The program should add a phone number to the contact and print it.

contact = {"name": "Leo"}
contact["phone"] == "555-0100"
print(contact["phone"])   # 555-0100

Solution 5.9.5 · ex_5_9_5.py

Variables and Types

Exercise 5.10.1 — Reading a number

Input arrives as text. The program should turn “25” into a number and print 30 after adding 5.

age_text = "25"
age = age_text + 5
print(age)   # 30

Solution 5.10.1 · ex_5_10_1.py

Exercise 5.10.2 — Building a message

The program should combine a label and a number into one sentence: “Score: 90”.

score = 90
message = "Score: " + score
print(message)   # Score: 90

Solution 5.10.2 · ex_5_10_2.py

Exercise 5.10.3 — Checking a type

The program should report the type of a price as float.

price = 3.99
print(type(price))   # <class 'float'>
print(type(price) == int)   # expected: True

Solution 5.10.3 · ex_5_10_3.py

Exercise 5.10.4 — Converting to float

The program should turn the text “2.5” into a float and print double it, 5.0.

weight_text = "2.5"
weight = int(weight_text)
print(weight * 2)   # 5.0

Solution 5.10.4 · ex_5_10_4.py

Exercise 5.10.5 — Whole-number average

Two test scores are 80 and 91. The program should print their average as a whole number, 85.

score1 = 80
score2 = 91

average = str((score1 + score2) / 2)
print(int(average))   # 85

Solution 5.10.5 · ex_5_10_5.py