CPSC120B - Day 25 Notes

Cool Computer Science Thing of the Day

Monkeys Regain Control of Paralyzed Legs With Help of an Implant

Reading Questions

Quiz

Quiz 25

Dictionaries

Lists are ordered collections, data is access according to where it is located (using the index operator)
Dictionaries are unordered, so when creating a dictionary a ‘look up’ or key must be specified for each value
```
a_dict = {1: 'one', 3: 'three'}
print(a_dict[1])
```
They are called dictionaries because they are like language dictionaries, which associate words with definitions

The keys can be any immutable type, the values can be any type

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
print(a_dict['butyraceous'])

Note, you can only look up using keys, not values

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
print(a_dict['buttery']) # an error there is no key buttery

Dictionaries are mutable

Can change a value by assigning

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
a_dict['butyraceous'] = 'like butter'
print(a_dict['butyraceous'])

Can create new entries by assigning to keys that are not already in the dictionary

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
a_dict['Pickwickian'] = 'odd or unusual'
print(a_dict['Pickwickian'])

Can remove from a dictionary by using del

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
del a_dict['butyraceous']
print(a_dict['butyraceous']) # an error

Dictionary Iteration

Can iterate over the keys of a dictionary

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
for key in a_dict:
    print(a_dict)

Can iterate over the values, by using the keys

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
for key in a_dict:
    print(a_dict[key])

Note, the order of keys during iteration is not easily predictable and may change
The dictionary is stored in a form that makes access fast

If you need to iterate in an order, can create a list of keys, order the list, and use it to iterate

a_dict = {'butyraceous': 'buttery', 'inutile': 'no use'}
keys = list(a_dict.keys())
keys.sort()
for i in range(len(keys)):
    key = keys[i]
    print(key, ":", a_dict[key])

String Split

    a_string = 'this is a string'
    a_list = a_string.split()
    print(a_list)

Lab

Queue
lab25