Collections Basics 2

After getting our handy dirty with lists we do another round of exercises, now focusing on dictionaries. We will once again go over how to:

• Create a dictionary with data
• Append, access and remove elements
• Loop over dictionary elements

Usage

Dictionaries (also called dicts) of course can also be stored in variables. For example let's store fruits, grouped by their color:

fruits = {
  'red': ['apple', 'cherry', 'strawberry'],
  'orange':['orange', 'mango', 'peach'],
  'yellow': ['banana', 'lemon']
}

Elements in this dictionary can be accessed by keys which are Strings. For example all red fruits can be accessed using fruits['red']. The nested value apple could be accessed using fruits['red'][0].

To add an element to or update one in a dictionary you can use the key syntax as well or use the update method:

fruits['green'] = ['watermelon']
fruits.update({'green': ['watermelon']})

To remove an element from a dictionary one can use the pop method with a specified key. For example to remove all yellow fruits:

fruits.pop('yellow')

You can also loop over dictionaries like you can loop over lists using the items method:

for color, colored_fruits in fruits.items()
  print(color + ' fruits:')
  for fruit in colored_fruits:
    print('- ' + fruit)

Tasks

Task 1

Create a variable called person which should hold a dictionary. The dictionary should have the key name with the value Bart Simpson and the key address with the value 742 Evergreen Terrace. Print the name and the address separated by comma to the screen.

• Your result should look like this:

Bart Simpson, 742 Evergreen Terrace

Task 2

Create two variables one called bart and the other called homer. Each stores a dictionary, one with the key name and the value Bart Simpson, the other one with the same key but the value Homer Simpson. Create a third variable address with a dictionary which only has one key address.

Use update to add the address to both bart and homer. Print bart['address'] to the screen.

• Your result should look like this:

742 Evergreen Terrace

Task 3

Create a variable ages which holds a dictionary with the key Peter and the value 36, the key Robin and the value 29 and the key Michael with the value 33. Loop over the dictionary and print the name with the age.

• Your result should look like this:

Peter is 36 years old
Robin is 29 years old
Michael is 33 years old

Task 4

Store the animals Alligator, Tiger, Parrot, Hamster, and Dolphin as keys in a dict. Use random numbers as values. Now remove all keys ending with r from the dictionary and print the resulting dict to the screen.

• Your result should look similar to this:

{'Dolphin': 8, 'Parrot': 2}