Review

• Functions
• Method calls
• Data Type: Dictionaries

What we will cover for the rest of today

• (Even) More Data Types
• Combining data types

Data Type: Sets

Sets are unordered data types whose elements are unique. Therefore, adding a value to a set that already has it, does nothing.

Sets can be created with comma separated elements enclosed in {} in Python 2.7 or greater.

Very often, one will make a list and use the set() function to eliminate duplicates.

>>> list_a = [0, 3, 2, 0, 2, 7]
>>> set_a = set(list_a)
>>> print set_a
set([0, 2, 3, 7])

>>> set_b = {1, 2, 1, 3}
>>> print set_b
set([1, 2, 3])
            

Sets have an add method, which like append for lists, adds an element to a set.

Data Type: Lists of ... Lists

As we have already seen, an element in a list can be other lists.

Lists inside of a list are referred to as nested

game_board = [
    ['O', 'X', ' '],
    [' ', 'X', ' '],
    [' ', ' ', ' '],
]
            

This can be indexed successively with game_board[0][1]

Nested Lists continued

A list can be appended to a list as well

mary_shopping_list = ['apples', 'bananas', 'chicken', 'ice cream']
fran_shopping_list = ['ice cream', 'beef', 'peppers', 'apples']
bob_shopping_list = ['chicken', 'peppers']

family_shopping_list = []
family_shopping_list.append(mary_shopping_list)
family_shopping_list.append(fran_shopping_list)
family_shopping_list.append(bob_shopping_list)

print family_shopping_list

for shop_list in family_shopping_list:
    for food_item in shop_list:
        print food_item
            

What if we want to flatten the family shopping list?

What if we want the food items in the family shopping list to be unique?

Lists of Dictionaries

One of the most common and useful nested data structures,
is a list of dictionaries

card_a = {
    'suit': 'spades',
    'number': 4,
}

card_b = {
    'suit': 'hearts',
    'number': 8,
}

hand = [card_a, card_b]

print 'The hand contains:'
for card in hand:
    print 'A', card['number'], 'of', card['suit']
            

Dictionary of Lists

A dictionary can also contain values that are themselves
other data types, such as lists.

mary_shopping_list = ['apples', 'bananas', 'chicken', 'ice cream']
fran_shopping_list = ['ice cream', 'beef', 'peppers', 'apples']
bob_shopping_list = ['chicken', 'peppers']

family_shopping_list = {
    'mary': mary_shopping_list,
    'fran': fran_shopping_list,
    'baby': bob_shopping_list,
}

for name, shop_list in family_shopping_list.items():
    print name, 'needs to buy: ', shop_list

# Changing this later can be accomplished with
family_shopping_list['fran'].append('strawberries')
            

Now the to do lists can be indexed or modified by name

Means of Combination

Lists, dictionaries, and other data types are all
a means of combination.

They can be freely combined to create the
data structure needed for a particular problem.

all_tweets = [
    {
        'author': 'mary',
        'handle': '@hadalittlelamb',
        'date': '2013-01-22',
        'tweets': [
            'at Loco Pops enjoying a Raspberry Sage popsicle',
            'Learning Python is so much fun',
        ],
    },
]
            

Functions on Dictionaries

character = {
    'level': 'beginner',
    'health': 100,
}

def injure(character, damage):
    character['health'] = character['health'] - damage
    if character['health'] < 0:
        character['health'] = 0

def heal(character, amount):
    character['health'] = character['health'] + amount
    if character['health'] > 100:
        character['health'] = 100
                  

Functional Python: Map

Python is a not a purely functional language, but it can be used (and is commonly used) for functional programming.

There are four functions that are used for functional programming: Range, Filter, Map, and Reduce

One commonly used, higher order function
(that is a Python builtin) is called map

# Define any function
def sqaure(number):
    return number ** 2

# Pass the function to map along with an iterable
squares = map(square, range(10))
                    

Let's Develop It

Write a function that prints the double
of every number from 0 to 10 using a for loop

Write a function that prints the double
of every number from 0 to 10 using a range

Write a function that prints the double
of every number from 0 to 10 using a map

Write a map that takes in a list and appends "or I'll be a monkey's uncle" to every item in that list. (input: [1,4], output: ["1 or I'll be a monkey's uncle"], "2 or I'll be a monkey's uncle"])

Let's Develop It

Choose among any of these projects:
(Resources available on the next page)

• Search the Web - Write a program that searches the web
  using DuckDuckGo and displays results.
• Encryption - Write a program that encrypts a string from
  user input, or file and is able to decrypt it as well.
• Command Line Game - Create a simple game that runs inside the terminal.

Let's Develop It Resources

Let's Develop It Resources Continued

Future Resources

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