COMP1531

2.2 - Python - Dictionaries

Python - Dictionaries

Lists are sequential containers of memory. Values are referenced by their integer index (key) that represents their location in an order

Python - Dictionaries

Dictionaries are associative containers of memory. Values are referenced by their string key that maps to a value

name

"sally"

age

height

"187cm"

Python - Dictionaries

Dictionaries are associative containers of memory. Values are referenced by their string key that maps to a value

userData = {}
userData["name"] = "Sally"
userData["age"] = 18
userData["height"] = "187cm"
print(userData)

{'name': 'Sally', 'age': 18, 'height': '187cm'}

dict_basic_1.py

Python - Dictionaries

There are a number of different ways we can construct and interact with dictionaries

userData = {
  'name' : 'Sally',
  'age' : 18,
  'height' : '186cm', # Why a comma?
}
userData['height'] = '187cm'
print(userData)

{'name': 'Sally', 'age': 18, 'height': '187cm'}

dict_basic_2.py

Python - Dictionaries

Basic loops are over keys not values:

How would we modify this to print out the values instead?

userData = [
    {
        'name' : 'Sally',
        'age' : 18,
        'height' : '186cm',
    }, {
        'name' : 'Bob',
        'age' : 17,
        'height' : '188cm',
    },
]
for user in userData:
    print("Whole user: ", user)
    for part in user:
        print(f"  {part}")

Whole user:  {'name': 'Sally', 'age': 18, 'height': '186cm'}
  name
  age
  height
Whole user:  {'name': 'Bob', 'age': 17, 'height': '188cm'}
  name
  age
  height

dict_loop.py

Python - Dictionaries

userData = {'name' : 'Sally','age' : 18, \
            'height' : '186cm'}

for user in userData.items():
    print(user)
print("====================")

for user in userData.keys():
    print(user)

print("====================")
for user in userData.values():
    print(user)

('name', 'Sally')
('age', 18)
('height', '186cm')
====================
name
age
height
====================
Sally
18
186cm

dict_loop_2.py

Python - Dictionaries

Optional Activity

Q. Write a python program that takes in a series of words from STDIN and outputs the frequency of how often each vowel appears