1. 字典（dict）

字典是一系列键值对

1.1 创建字典

# 空字典
person = {}

# 添加 or 更新键值对
person['name'] = 'Alice'
print(person)

person = {'name': 'Alice', 'age': 25}

languages = {
    'Alice': ['Java', 'Python'],
    'Alan': ['Python'],
    'Tom': ['Go', 'Java']
}

1.2 访问字典值

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

print(f'alien["color"]:{alien["color"]}, alien["points"]:{alien["points"]}')

当 key 不存在时，会报错 KeyError

print(alien['other'])
# KeyError: 'other'

改进 get(key, default)
key: 键，必填
default：键不存在时返回的默认值，可选

other = alien.get('other')
other_default = alien.get('other', 'not exist')
other_default2 = alien.get('other', '')
print(f'other: {other}, other_default: {other_default}')

1.3 字典操作

字典是一种动态结构，可随时在其中添加键值对

alien = {}
alien['x_point'] = 0
alien['y_point'] = 10

alien['name'] = 'axis'
# 删除键值对
del alien['name']

1.4 字典遍历

def dict_loop():
    languages = {
        'Alice': 'Java',
        'Alan': 'Python',
        'Tom': 'Go'
    }

    # 遍历字典
    for item in languages.items():
        print(item)

    for i, item in enumerate(languages.items()):
        print(i, item)

    for key, value in languages.items():
        print(f'key: {key}, value: {value}')

    # 遍历键
    for key in languages.keys():
        print(f'key: {key.title()}')
    # 等价，省略 .keys()
    for key in languages:
        print(key.title())

    # 遍历值
    for value in languages.values():
        print(value)

1.5 排序

languages = {
    'Alice': 'Java',
    'Alan': 'Python',
    'Tom': 'Go'
}

if 'Alan' in languages.keys():
    print('Alan is in languages.keys() \n')

# 排序，sorted(*args) 不会修改原数据
sorted_languages = sorted(languages.keys())
print(sorted_languages)

duplicate_data = ['aaa', 'bbb', 'aaa', 'ccc']
# set去重（不保证原顺序）
set_data = set(duplicate_data)
print(set_data)
print(duplicate_data)

# 保留插入顺序（Python 3.7+）
unique_data = list(dict.fromkeys(duplicate_data))
print(unique_data)
print(duplicate_data)

1.6 字典集合

aliens = []
for e in range(3):
    new_alien = {'color': 'green', 'points': e}
    aliens.append(new_alien)
print(aliens)

[
    {'color': 'green', 'points': 0}, 
    {'color': 'green', 'points': 1}, 
    {'color': 'green', 'points': 2}
]

1.7 字典中存储 对象 + 列表

languages = {
    'Alice': ['Java', 'Python'],
    'Alan': ['Python'],
    'Tom': ['Go', 'Java']
}
for key, item in languages.items():
    print(f'key: {key}, item: {item}')
    for e in item:
        print('\t', e)

1.8 字典中存储字典

users = {
    'Alan': {
        'career': 'Master',
        'language': 'Python'
    },
    'Alice': {
        'career': 'Programmer',
        'language': 'Java'
    }
}

print(users.get('Alan'))

for key, item in users.items():
    print(f'key: {key}, career: {item.get("career")}, language: {item.get("language")}')