Chapter 6 Dictionaries

6.1 A simple Dictionary


alien_0 = {'color': 'green', 'points': 5}
print(alien_0)


print(alien_0['color'])
print(alien_0['points'])

6.2 Working with dictionaries


alien_0 = {'color': 'green'}

6.2.1 Accessing values in dictionary


alien_0 = {'color': 'green'}
print(alien_0['color'])


alien_0 = {'color': 'green', 'points': 5}

new_points = alien_0['points']
print(f'You just earned {new_points} points!')



## 6.2.2 Adding new key-value pairs

```python

alien_0 = {'color': 'green', 'points': 5}
print(alien_0)

alien_0['x_position'] = 0
alien_0['y_position'] = 25
print(alien_0)

6.2.3 Starting with an empty dictionary


alien_0 = {}

alien_0['color'] = 'green'
alien_0['points'] = 5

print(alien_0)

6.2.4 Modifying values in a dictionary


alien_0 = {'color': 'green'}
print(f"The alien is {alien_0['color']}.")

alien_0['color'] = 'yellow'
print(f"The alien is now {alien_0['color']}.")


alien_0 = {'x_position': 0, 'y_position': 25, 'speed': 'medium'}
print(f"Original x-position: {alien_0['x_position']}")

if alien_0['speed'] == 'slow':
    x_increment = 1
elif alien_0['speed'] == 'medium':
    x_increment = 2
else:
    x_increment = 3
alien_0['x_position'] = alien_0['x_position'] + x_increment
print(f"New position: {alien_0['x_position']}")


alien_0 = {'x_position': 0, 'y_position': 25, 'speed': 'medium'}
alien_0['speed'] = 'fast'
print(f"Original x-position: {alien_0['x_position']}")

if alien_0['speed'] == 'slow':
    x_increment = 1
elif alien_0['speed'] == 'medium':
    x_increment = 2
else:
    x_increment = 3
alien_0['x_position'] = alien_0['x_position'] + x_increment
print(f"New position: {alien_0['x_position']}")

6.2.5 Removing key-value pairs


alien_0 = {'color': 'green', 'points': 5}
print(alien_0)

del alien_0['points']
print(alien_0)

6.2.6 A dicitonary of similar objects


favorite_languages = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}

language = favorite_languages['sarah'].title()
print(f"Sarah's favorite language is {language}")

需要注意：字典最后一个键值对会面一般会有一个“,”，这样在以后修改字典时，不易发生忘记逗号的错误。但其实，有没有逗号都是可以的。

6.2.7 Using get() to access values


alien_0 = {'color': 'green', 'speed': 'slow'}
print(alien_0['points'])


alien_0 = {'color': 'green', 'speed': 'slow'}

point_value = alien_0.get('points', 'No point value assigned.')
print(point_value)

TRY IT YOURSELF

person.py
favorite_numbers.py
glossary.py

6.3 Looping through a dictionary

6.3.1 Looping throught all key-value pairs


user_0 = {
    'username': 'efermi',
    'first': 'enrico',
    'last': 'fermi',
}


for key, value in user_0.items():
    print(f'\nKey:{key}')
    print(f'Value:{value}')


favorite_languages = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}

for name, language in favorite_languages.items():
    print(f"{name.title()}'s favorite language is {language.title()}.")

6.3.2 Looping through all keys in a dictionary


for name in favorite_languages.keys():
    print(name.title())


for name in favorite_languages:
    print(name.title())


friends = ['phil', 'sarah']
for name in favorite_languages.keys():
    print(name.title())
    if name in friends:
        language = favorite_languages[name].title()
        print(f"\t{name.title()}, I see you love {language}!")


if 'erin' not in favorite_languages.keys():
    print("Erin, please take our poll!")

6.3.3 Looping through a dictionary’s keys in a particular order


for name in sorted(favorite_languages.keys()):
    print(f"{name.title()}, thank you for taking the poll.")

6.3.4 Looping through all values in a dictionary


print("The following languages have been mentioned:")
for language in favorite_languages.values():
    print(language.title())


print("The following languages have been mentioned:")
for language in set(favorite_languages.values()):
    print(language.title())

TRY IT YOURSELF

glossary_2.py
rivers.py
polling.py

6.4 Nesting

6.4.1 A list of dictionaries


alien_0 = {'color': 'green', 'points': 5}
alien_1 = {'color': 'yellow', 'points': 10}
alien_2 = {'color': 'red', 'points': 15}

aliens = [alien_0, alien_1, alien_2]

for alien in aliens:
    print(alien)


aliens = []

for alien_number in range(30):
    new_alien = {'color': 'green', 'points': 5, 'speed': 'slow'}
    aliens.append(new_alien)

for alien in aliens[:5]:
    print(alien)
print("...")

print(f"Total number of aliens: {len(aliens)}")


aliens = []

for alien_number in range(30):
    new_alien = {'color': 'green', 'points': 5, 'speed': 'slow'}
    aliens.append(new_alien)

for alien in aliens[:3]:
    if alien['color'] == 'green':
        alien['color'] = 'yellow'
        alien['speed'] = 'medium'
        alien['points'] = 10
        
for alien in aliens[:5]:
    print(alien)
        
print("...")

6.4.2 A list in a dictionaries


pizza = {
    'crust': 'thick',
    'toppings': ['mushrooms', 'extra cheese'],
}

print(f"You ordered a {pizza['crust']}-crust pizza "
      "with the following toppings:")
for topping in pizza['toppings']:
    print("\t" + topping)


favorite_languages = {
    'jen': ['python', 'ruby'],
    'sarah': ['c'],
    'edward': ['ruby', 'go'],
    'phil': ['python', 'haskell'],
}
for name, languages in favorite_languages.items():
    print(f"\n{name.title()}'s favorite languages are:")
    for language in languages:
        print(f"\t{language.title()}")

6.4.3 A dictionary in a dictionary


users = {
    'aeinstein': {
        'first': 'albert',
        'last': 'einstein',
        'location': 'princeton',
    },
    'mcurie': {
        'first': 'marie',
        'last': 'curie',
        'location': 'paris',
    },
    }
for username, user_info in users.items():
    print(f"\nUsername: {username}")
    full_name = f"{user_info['first']} {user_info['last']}"
    location = user_info['location']
    print(f"\tFull name: {full_name.title()}")
    print(f"\tLocation: {location.title()}")