This document provides an introduction to dictionaries in Python. It explains that dictionaries are collections of key-value pairs that allow users to store, query, add, update, and delete information. It shows how to initialize an empty dictionary and populate it with initial key-value pairs. It also demonstrates how to query, add, update, and delete key-value pairs from a dictionary. Finally, it provides a phone book example to demonstrate using dictionaries in a practice program.

1. Dictionary
Python Built-in Data Type

2. What does Dict do?
• Collection of information
• Query information
• Add/Update Information
Dictionary
Introduction

3. Initialization
• aDict = {}
• aDict = dict()
• aDict = { “apple” : 3
“banana”: 5 }
Dictionary
Introduction

4. Initialization
• aDict = {}
• aDict = dict()
• aDict = { “apple” : 3
“banana”: 5 }
Key
Dictionary
Introduction

5. Initialization
• aDict = {}
• aDict = dict()
• aDict = { “apple” : 3
“banana”: 5 }
Key Value
Dictionary
Introduction

6. Query
>>> aDict["apple"]
3
>>> aDict.keys()
dict_keys(['apple', 'banana'])
>>> aDict.values()
dict_values([3, 5])
>>> aDict.items()
dict_items([('apple', 3), ('banana', 5)])
Dictionary
Introduction

7. Query
• Call each item with for-loop statement
>>> for x in aDict.keys():
... print(x)
...
apple
banana
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Introduction

8. Add
• Directly add a item to dictionary
>>> aDict
{'apple': 5, 'banana': 5}
>>> aDict['waterfruit'] = 8
>>> aDict
{'waterfruit': 8, 'apple': 5, 'banana': 5}
Dictionary
Introduction

9. Update
• Update the content of the dictionary
• aDict.update(<dict>)
• Example:
>>> aDict.update({'apple':5})
>>> aDict.update({'chocolate':10})
>>> aDict
{'chocolate': 10, 'apple': 5, 'banana': 5}
Dictionary
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10. Delete
• Remove a item from the dictionary
• del aDict[“apple”]
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11. Practice
• Phone book
• Functions:
• Print a phone number
• Add a phone number
• Remove a phone number
• Lookup a phone number
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12. Practice
def print_menu():
print('1. Print Phone Numbers')
print('2. Add a Phone Number')
print('3. Remove a Phone Number')
print('4. Lookup a Phone Number')
print('5. Quit')
print()
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13. Practice
numbers = {}
menu_choice = 0
print_menu()
while menu_choice != 5:
menu_choice = int(input("Type in a number (1-5): "))
if menu_choice == 1:
pass
elif menu_choice == 2:
pass
elif menu_choice == 3: http://goo.gl/A9xDr
pass
elif menu_choice == 4:
pass
elif menu_choice != 5:
print_menu()
Dictionary
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14. Print
if menu_choice == 1:
print("Telephone Numbers:")
for x in numbers.keys():
print("Name: ", x, "tNumber:", numbers[x])
print()
Dictionary
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15. Add
elif menu_choice == 2:
print("Add Name and Number")
name = input("Name: ")
phone = input("Number: ")
numbers[name] = phone
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16. Remove
elif menu_choice == 3:
print("Remove Name and Number")
name = input("Name: ")
if name in numbers:
del numbers[name]
else:
print(name, "was not found")
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17. Lookup
elif menu_choice == 4:
print("Lookup Number")
name = input("Name: ")
if name in numbers:
print("The number is", numbers[name])
else:
print(name, "was not found")
Dictionary
Introduction