{python}

Introduction to Python - Lecture 6

Zohair ul Hasan

Summary

  • Lists can store multiple values
  • Lists are mutable
  • Tuple and strings are immutable

Recap

Yesterday's homework

Today's Lecture

Dictionaries

The Dictionary Data type

Like a list, a dictionary is a mutable collection of many values

But unlike indexes for lists, indexes for dictionaries can use many different data types, not just integers

The Dictionary Data type

Indexes for dictionaries are called keys, and a key with its associated value is called a key-value pair.  

The Dictionary Data type

>>> myCat = {'size': 'fat', 'color': 'gray', 'disposition': 'loud'}
>>> myCat['size']
'fat'
>>> 'My cat has ' + myCat['color'] + ' fur.'
'My cat has gray fur.'
>>> spam = {12345: 'Luggage Combination', 42: 'The Answer'}

Dictionaries are unordered

>>> spam = ['cats', 'dogs', 'moose']
>>> bacon = ['dogs', 'moose', 'cats']
>>> spam == bacon
False
>>> eggs = {'name': 'Zophie', 'species': 'cat', 'age': '8'}
>>> ham = {'species': 'cat', 'age': '8', 'name': 'Zophie'}
>>> eggs == ham
True

KeyError

>>> spam = {'name': 'Zophie', 'age': 7}
>>> spam['color']
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    spam['color']
KeyError: 'color'

Birthday Program

birthdays = {'Alice': 'Apr 1', 'Bob': 'Dec 12', 'Carol': 'Mar 4'}

   while True:
       print('Enter a name: (blank to quit)')
       name = input()
       if name == '':
           break

       if name in birthdays:
           print(birthdays[name] + ' is the birthday of ' + name)
       else:
           print('I do not have birthday information for ' + name)
           print('What is their birthday?')
           bday = input()
           birthdays[name] = bday
           print('Birthday database updated.')

Birthday Program

Enter a name: (blank to quit)
Alice
Apr 1 is the birthday of Alice
Enter a name: (blank to quit)
Eve
I do not have birthday information for Eve
What is their birthday?
Dec 5
Birthday database updated.
Enter a name: (blank to quit)
Eve
Dec 5 is the birthday of Eve
Enter a name: (blank to quit)

The keys(), values(), and items() Methods

>>> myCat = {'size': 'fat', 'color': 'gray', 'disposition': 'loud'}
>>> type(myCat.keys())
<class 'dict_keys'>
>>> type(myCat.values())
<class 'dict_values'>
>>> type(myCat.items())
<class 'dict_items'>
>>> spam = {'color': 'red', 'age': 42}
>>> for v in spam.values():
...     print(v)

red
42

The keys(), values(), and items() Methods

>>> for k in spam.keys():
...     print(k)

color
age
>>> for i in spam.items():
...     print(i)

('color', 'red')
('age', 42)

The keys(), values(), and items() Methods

>>> spam = {'color': 'red', 'age': 42}
>>> spam.keys()
dict_keys(['color', 'age'])
>>> list(spam.keys())
['color', 'age']

The keys(), values(), and items() Methods

>>> spam = {'color': 'red', 'age': 42}
>>> for k, v in spam.items():
...     print('Key: ' + k + ' Value: ' + str(v))

Key: age Value: 42
Key: color Value: red

Checking Whether a Key or Value Exists in a Dictionary

>>> spam = {'name': 'Zophie', 'age': 7}
>>> 'name' in spam.keys()
True
>>> 'Zophie' in spam.values()
True
>>> 'color' in spam.keys()
False
>>> 'color' not in spam.keys()
True
>>> 'color' in spam
False

The get() Method

>>> picnicItems = {'apples': 5, 'cups': 2}
>>> 'I am bringing ' + str(picnicItems.get('cups', 0)) + ' cups.'
'I am bringing 2 cups.'
>>> 'I am bringing ' + str(picnicItems.get('eggs', 0)) + ' eggs.'
'I am bringing 0 eggs.'

The get() Method

>>> picnicItems = {'apples': 5, 'cups': 2}
>>> 'I am bringing ' + str(picnicItems['eggs']) + ' eggs.'
Traceback (most recent call last):
  File "<pyshell#34>", line 1, in <module>
    'I am bringing ' + str(picnicItems['eggs']) + ' eggs.'
KeyError: 'eggs'

Pretty Printing Dictionaries

>>> import pprint
>>> my_dict = { "key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4", "key5": "value5", "key6": "value6", "key7": "value7", "key8": "value8", "key9": "value9"}
>>> print(my_dict)
{'key1': 'value1', 'key2': 'value2', 'key3': 'value3', 'key4': 'value4', 'key5': 'value5', 'key6': 'value6', 'key7': 'value7', 'key8': 'value8', 'key9': 'value9'}
>>> pprint.pprint(my_dict)
{'key1': 'value1',
 'key2': 'value2',
 'key3': 'value3',
 'key4': 'value4',
 'key5': 'value5',
 'key6': 'value6',
 'key7': 'value7',
 'key8': 'value8',
 'key9': 'value9'}

Tic-Tac-Toe

Tic-Tac-Toe

theBoard = {
    "top-L": " ",
    "top-M": " ",
    "top-R": " ",
    "mid-L": " ",
    "mid-M": " ",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": " ",
}

Tic-Tac-Toe

Tic-Tac-Toe

theBoard = {
    "top-L": " ",
    "top-M": " ",
    "top-R": " ",
    "mid-L": " ",
    "mid-M": "X",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": " ",
}

Tic-Tac-Toe

Tic-Tac-Toe

theBoard = {
    "top-L": "O",
    "top-M": "O",
    "top-R": "O",
    "mid-L": "X",
    "mid-M": "X",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": "X",
}

Tic-Tac-Toe

Tic-Tac-Toe

theBoard = {
    "top-L": " ",
    "top-M": " ",
    "top-R": " ",
    "mid-L": " ",
    "mid-M": " ",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": " ",
}


def printBoard(board):
    print(board["top-L"] + "|" + board["top-M"] + "|" + board["top-R"])
    print("-+-+-")
    print(board["mid-L"] + "|" + board["mid-M"] + "|" + board["mid-R"])
    print("-+-+-")
    print(board["low-L"] + "|" + board["low-M"] + "|" + board["low-R"])


printBoard(theBoard)

Tic-Tac-Toe

 | |
-+-+-
 | |
-+-+-
 | |

Tic-Tac-Toe

theBoard = {
    "top-L": "O",
    "top-M": "O",
    "top-R": "O",
    "mid-L": "X",
    "mid-M": "X",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": "X",
}


def printBoard(board):
    print(board["top-L"] + "|" + board["top-M"] + "|" + board["top-R"])
    print("-+-+-")
    print(board["mid-L"] + "|" + board["mid-M"] + "|" + board["mid-R"])
    print("-+-+-")
    print(board["low-L"] + "|" + board["low-M"] + "|" + board["low-R"])


printBoard(theBoard)

Tic-Tac-Toe

O|O|O
-+-+-
X|X|  
-+-+-
 | |X

Tic-Tac-Toe

theBoard = {
    "top-L": " ",
    "top-M": " ",
    "top-R": " ",
    "mid-L": " ",
    "mid-M": " ",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": " ",
}

def printBoard(board):
    print(board["top-L"] + "|" + board["top-M"] + "|" + board["top-R"])
    print("-+-+-")
    print(board["mid-L"] + "|" + board["mid-M"] + "|" + board["mid-R"])
    print("-+-+-")
    print(board["low-L"] + "|" + board["low-M"] + "|" + board["low-R"])

turn = "X"
for i in range(9):
    printBoard(theBoard)
    print("Turn for " + turn + ". Move on which space?")
    move = input()
    theBoard[move] = turn
    if turn == "X":
        turn = "O"
    else:
        turn = "X"
printBoard(theBoard)

Tic-Tac-Toe

theBoard = {
    "top-L": " ",
    "top-M": " ",
    "top-R": " ",
    "mid-L": " ",
    "mid-M": " ",
    "mid-R": " ",
    "low-L": " ",
    "low-M": " ",
    "low-R": " ",
}

def printBoard(board):
    print(board["top-L"] + "|" + board["top-M"] + "|" + board["top-R"])
    print("-+-+-")
    print(board["mid-L"] + "|" + board["mid-M"] + "|" + board["mid-R"])
    print("-+-+-")
    print(board["low-L"] + "|" + board["low-M"] + "|" + board["low-R"])

turn = "X"
for i in range(9):
    printBoard(theBoard)
    print("Turn for " + turn + ". Move on which space?")
    move = input()
    theBoard[move] = turn
    if turn == "X":
        turn = "O"
    else:
        turn = "X"
printBoard(theBoard)

Tic-Tac-Toe

 | |
-+-+-
 | |
-+-+-
 | |
Turn for X. Move on which space?
mid-M
 | |
-+-+-
 |X|  
-+-+-
 | |

--snip--

O|O|X
-+-+-
X|X|O
-+-+-
O| |X
Turn for X. Move on which space?
low-M
O|O|X
-+-+-
X|X|O
-+-+-
O|X|X

Nested Dictionaries and Lists

allGuests = {
    "Alice": {"apples": 5, "pretzels": 12},
    "Bob": {"ham sandwiches": 3, "apples": 2},
    "Carol": {"cups": 3, "apple pies": 1},
}


def totalBrought(guests, item):
    numBrought = 0
    for k, v in guests.items():
        numBrought = numBrought + v.get(item, 0)
    return numBrought


print("Number of things being brought:")
print(" - Apples         " + str(totalBrought(allGuests, "apples")))
print(" - Cups           " + str(totalBrought(allGuests, "cups")))
print(" - Cakes          " + str(totalBrought(allGuests, "cakes")))
print(" - Ham Sandwiches " + str(totalBrought(allGuests, "ham sandwiches")))
print(" - Apple Pies     " + str(totalBrought(allGuests, "apple pies")))

Nested Dictionaries and Lists

 Number of things being brought:
 - Apples 7
 - Cups 3
 - Cakes 0
 - Ham Sandwiches 3
 - Apple Pies 1

Quiz!

Activity

Complete the activity at https://itp.zohair.dev/activities/fantasy-game-inventory