Dictionaries and Structuring Data
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 vs. Lists
>>> 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
>>> spam = {'name': 'Zophie', 'age': 7}
>>> spam['color']
Traceback (most recent call last):
File "<pyshell#1>", line 1, in <module>
spam['color']
KeyError: 'color'
The keys(), values(), and items() Methods
>>> spam = {'color': 'red', 'age': 42}
>>> for v in spam.values():
print(v)
red
42
>>> for k in spam.keys():
print(k)
color
age
>>> for i in spam.items():
print(i)
('color', 'red')
('age', 42)
-
the values in the dict_items value returned by the items() method are tuples of the key and value.
-
If you want a true list from one of these methods, pass its list-like return value to the list() function.
>>> spam = {'color': 'red', 'age': 42}
>>> spam.keys()
dict_keys(['color', 'age'])
>>> list(spam.keys())
['color', 'age']
>>> 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
- 'color' in spam is essentially a shorter version of writing 'color' in spam.keys().
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 setdefault() Method
Pretty Printing
Using Data Structures to Model Real-World Things
A Tic-Tac-Toe Board
Nested Dictionaries and Lists
Fantasy Game Inventory
stuff = {'rope': 1, 'torch': 6, 'gold coin': 42, 'dagger': 1, 'arrow': 12}
def displayInventory(inventory):
print("Inventory:")
item_total = 0
for k, v in inventory.items():
print(str(v) + ' ' + k)
item_total = item_total + v
print("Total number of items: " + str(item_total))
displayInventory(stuff)