Python中的字典及其使用方法

fruit = {'name': 'apple', 'color': 'red', 'num': 5}  #有三个键值对的字典
print('name: ' + fruit['name']) #打印每个键所对应的值
print('color: ' + fruit['color'])
print('num: ' + str(fruit['num']))

fruit = {}  #创建一个空字典
print('1.fruit = ' + str(fruit))
fruit['name'] = 'apple'  #依次添加键值对
print('2.fruit = ' + str(fruit))
fruit['color'] = 'red'
print('3.fruit = ' + str(fruit))
fruit['num'] = 5
print('4.fruit = ' + str(fruit))

fruit = {'name': 'apple', 'color': 'red', 'num': 5}
print('Before modify: fruit = ' + str(fruit))

fruit['color'] = 'green' #修改键名为'color'的值
fruit['num'] = 20  #修改键名为'num'的值
print('After modify: fruit = ' + str(fruit))

fruit = {'name': 'apple', 'color': 'red', 'num': 5}
print('Before delete: fruit = ' + str(fruit))

del fruit['color']  #删除键名为'color'的键值对
print('After delete: fruit = ' + str(fruit))

favorite_fruit = {
    'A': 'apple',
    'B': 'orange',
    'C': 'banana',
}
print("A's favorite fruit is " + favorite_fruit['A'] + ".")
print("B's favorite fruit is " + favorite_fruit['B'] + ".")
print("C's favorite fruit is " + favorite_fruit['C'] + ".")

favorite_fruit = {
    'A': 'apple',
    'B': 'orange',
    'C': 'banana',
}

for name, fruit in favorite_fruit.items():  #遍历字典中的所有键值对
    print(name + "'s favorite fruit is " + fruit + ".")

favorite_fruit = {
    'B': 'apple',
    'D': 'orange',
    'C': 'banana',
    'A': 'pear',
}

print('1. With .keys() output:')
for name in favorite_fruit.keys():  #遍历字典中所有的键
    print(name)

print('2. Without .keys() output:')  #遍历字典中所有的键——省略.keys()
for name in favorite_fruit:
    print(name)
 
print('3. sorted() output:')
for name in sorted(favorite_fruit.keys()):  #按顺序遍历字典中所有的键
    print(name)

favorite_fruit = {
    'B': 'apple',
    'D': 'orange',
    'C': 'banana',
    'A': 'apple',
}

print('1. All values output:')
for fruit in favorite_fruit.values():  #遍历字典中所有的值
    print(fruit)
    
print('2. With sorted() output:')
for fruit in sorted(favorite_fruit.values()):  #按顺序遍历字典中所有的值
    print(fruit)
    
print('3. With set() output:')
for fruit in set(favorite_fruit.values()):  #剔除重复的值
    print(fruit)

fruit_1 = {'name': 'apple', 'color': 'red', 'num': 15}
fruit_2 = {'name': 'banana', 'color': 'yellow', 'num': 10}
fruit_3 = {'name': 'watermelon', 'color': 'green', 'num': 20}
fruits = [fruit_1, fruit_2, fruit_3]  #将所有的字典存储在列表里
for fruit in fruits: #遍历列表
    print(fruit)

fruits = []  #创建一个空列表
for fruit_num in range(0,5): 
    new_fruit = {'name': 'apple', 'color': 'red', 'num': 10}
    fruits.append(new_fruit)

print('Before modify:')
for fruit in fruits:  #遍历列表
    print(fruit)

for fruit in fruits[:2]:  #修改列表中前2个元素的字典属性
    if fruit['color'] == 'red':
        fruit['color'] = 'green'
        fruit['num'] = 20

print('After modify:')
for fruit in fruits:  #遍历列表
    print(fruit)

favorite_fruit = {   #在字典中嵌套列表
    'A': ['apple', 'manGo'],
    'B': ['orange'],
    'C': ['banana', 'pear'],
}

for name, fruits in favorite_fruit.items():  #遍历字典中的键值对
    if len(fruits) == 1:  #列表的长度为1
        print(name+ "'s favorite fruits is :")
        for fruit in fruits:  #遍历字典中的列表
            print("\t" + fruit)
    else:  #列表的长度大于1
        print(name + "'s favorite fruits are :")
        for fruit in fruits:
            print("\t" + fruit)

users ={  #在字典中嵌套字典
    'user_1': {
        'first_name': 'lebron',
        'last_name': 'james',
    },
    'user_2': {
        'first_name': 'kobe',
        'last_name': 'bryant',
    },
    'user_3': {
        'first_name': 'kevin',
        'last_name': 'durant',
    },
}
for user, userinfo in users.items():  #遍历字典
    print(user + "'s name is " + userinfo['first_name'].title() + ' ' + userinfo['last_name'].title()+'.')