5. Lists¶

5.1. Preliminary exercises¶

5.1.1. Lists¶

You will learn the most from the exercises in this section, if you check your answers in this order: (1) check if you can find your answer in the reader, (2) try it out in a .py script or in the interactive window.

Exercise 5.1 List creation

How do you create an empty list?

How do you create a list with the three integers 1, 32, and 2?

Exercise 5.2. Given my_list = [30, 1, 12, 14, 10, 0]

How many items are in my_list?

What is the index of the first item in my_list?

What is the index of the last item in my_list?

What is my_list[2]?

What is my_list[-2]?

Exercise 5.3 What is the value of my_list after applying each of the following statements? Every statement starts with my_list = [5, 1, 2, 1, 0].

my_list.append(40)

my_list.insert(1, 43)

my_list.extend([1, 43])

my_list.remove(1)

my_list.sort()

my_list.reverse()

random.shuffle(my_list)

Exercise 5.4 Given my_list = [11, 5, 7, 5, 3], what is the value of var1 through var6 after the following statements?

var1 = my_list.index(3)

var2 = my_list.count(5)

var3 = len(my_list)

var4 = max(my_list)

var5 = min(my_list)

var6 = sum(my_list)

Exercise 5.5 What is the value of my_list after the following statements? Every statement starts with list1 = [5, 1, 2, 1, 0] and list2 = [1, 3, 6].

my_list = list1 + list2

my_list = 2 * list2

my_list = list2 * 2

my_list = list1[1 : 3]

my_list = list1[3]

Exercise 5.6 Write statements to do the following (in the ‘smart’ way):

Create a list with 20 values of 2.5.

Assign the value 5.5 to the last element in the list.

Display the sum of the first two elements.

Compute the sum of the first five elements in the list.

Find the minimum element in the list.

Randomly generate an index and display the element of this index in the list.

Exercise 5.7 What happens when your program attempts to access a list element with an invalid index (e.g. an index bigger than the number of items in the list)?

5.1.2. Repeating actions for all items in a list (for)¶

Exercise 5.8 Rewrite the following code so it uses a range instead of [0, 1, 2, 3, 4, 5].

for n in [0, 1, 2, 3, 4, 5]:
    print('I love to program!')

Exercise 5.9 Rewrite the following code using for - range instead of using a while.

n = 0
user_input = input("how many push-up do you want me to do? ")
nr_reps = int(user_input)
while n < nr_reps:
    print('push up!')
    n = n + 1

Exercise 5.10 What will the following code fragments display?

# 10a
for number in range(6):
    print(number)

# 10b
for number in range(2, 6):
    print(number)

# 10c
for number in range(0, 501, 100):
    print(number)

# 10d
for number in range(10, 5, -1):
    print(number)

Exercise 5.11 Suppose my_list = [‘apples’, ‘milk’, ‘cookies’, ‘bread’, ‘spaghetti’]. What will the following code fragments display?

# 11a
for item in my_list:
    print(item)

# 11b
for item in my_list:
    print(len(item * 2))

# 11c
for item in my_list[1:4]:
    if item == 'cookies':
        print('yummy!')
    else:
        print(item)

# 11d
my_list.reverse()
for item in my_list:
    print(item)

5.2. Programming exerises¶

Exercise 5.12 Suppose the student numbers of different studies at the TU/e have been recorded and stored in a list-of-lists nr_of_students:

nr_of_students = [
    ['study-year', 2014, 2015, 2016],
    ['Psy. & Tech.', 243, 298, 324],
    ['Informatics', 847, 939, 951],
    ['Mathematics', 148, 160, 194] ]

Write program fragments that:

print the nr of math students in 2014

print a list of all studies in nr_of_students

print the student nrs of ‘Informatics’ of all years in nr_of_students

print the nr of students of each study in 2015

prints the sum of numbers of students over the studies, for each separate year

Exercise 5.13 Magic Squares

Magic squares are squares with numbers from 1 to a certain number, that are ordered in such a way that the sum of each row, column and diagonal are equal. The picture below shows a well-known example of a magic square of size 3x3 (with numbers 1-9).

Squares like this can be encoded in a variable as a list-of-lists. Here is an example for the magic square in the figure above:

# example 1
square =  [[2, 7, 6], [9, 5, 1], [4, 3, 8]]

and another one that is not a magic square:

# example 2
square =  [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 16, 15]]

In all parts of this exercise your code should work correctly with any value of ‘square’ (without changing the rest of the code).

13a. Write a small program that prints the square as an aligned table.