3.5. Converting To Lists

It is often useful to convert variables in Python to a list so you can perform list operations. This can be achieved using list().

list(iterable)

Only iterables can be converted to a list. An iterable is a sequence of values you can go through.

Example: Convert a string to a list. This will create a list of characters that make up the given string.

text = 'Hello World!'
print(list(text))

['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!']

If we want to create a list of strings rather than characters we can use the .split() method.

The string is the text that you want to convert to a list and the separator is used to identify how the string should be broken up into different elements.

Example: Splitting on a space.

text = 'Red Orange Green Blue'
print(text.split(' '))

['Red', 'Orange', 'Green', 'Blue']

The separator you use doesn’t have to be a character, it can be a string.

Example: Splitting on a comma and a space.

weekdays = 'Monday, Tuesday, Wednesday, Thursday, Friday'
print(weekdays.split(', '))

['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']

Question 1

What do you think the output of the following code will be?

numbers = '12345678910'
print(list(numbers))

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 0]

['1', '2', '3', '4', '5', '6', '7', '8', '9', '10']

['1', '2', '3', '4', '5', '6', '7', '8', '9', '1', '0']

Solution

Python will treat numbers as a string. This means when it is convert to a list using list() it will create a list of characters. This means:

• The elements of the new list will be characters, not integers

• The last number, which is 10 will not be treated as a single number it will be broken up into the characters ‘1’ and ‘0’.

Question 2

What do you think the output of the following code will be?

fruits = 'apples,bananas,pears'
list_fruits = fruits.split(',')
print(list_fruits[1])

a

p

,

apples

bananas

pears

Solution

Solution is locked

Code challenge: String to List

Suppose you had the following string.

months = 'Jan-Feb-Mar-Apr-May-Jun-Jul-Aug-Sep-Oct-Nov-Dec'

Write a program to convert this string into a list and prints the result. Your output should look like this:

['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']

Solution

Solution is locked

Code challenge: Shopping List

Write a program that asks the user what they need to buy from the shops and converts this into a list of items. You can assume the user separates each item with a space.

Example 1

What do you need to buy? spaghetti tomatoes basil burrata
['spaghetti', 'tomatoes', 'basil', 'burrata']

Example 2

What do you need to buy? flour eggs milk sugar
['flour', 'eggs', 'milk', 'sugar']

Solution

Solution is locked

Code challenge: Secret Message

You want to send your friend a secret message. A simple way to do this is to put a jumble of characters between each letter you want to send. For example, if you want to send the message hello you might scramble this by placing the string "qmcsyd" between each letter. This means your secret message would look like this:

hqmcsydeqmcsydlqmcsydlqmcsydo

Write a program to decode this secret message. Your program should ask for the encrypted message and also for the string they used to scramble the message. You program should then return the decoded message.

Example 1

secret message: hqmcsydeqmcsydlqmcsydlqmcsydo
scramble string: qmcsyd
hello

Example 2

secret message: tkiblosekhkiblosekekiblosekrkiblosekekiblosek kiblosekakiblosekrkiblosekekiblosek kiblosekckiblosekokiblosekokiblosekkkiblosekikiblosekekiblosekskiblosek kiblosekikibloseknkiblosek kiblosektkiblosekhkiblosekekiblosek kiblosekckiblosekukiblosekpkiblosekbkiblosekokiblosekakiblosekrkiblosekd
scramble string: kiblosek
there are cookies in the cupboard

Solution

Solution is locked