# 创建一个空字典
empty_dict = {}
# 或者使用dict()函数
empty_dict = dict()

# 创建一个包含键值对的字典
student = {
    'name': '小明',
    'age': 15,
    'gender': '男',
    'grades': [85, 92, 78]
}

# 使用dict()函数创建字典
person = dict(name='小红', age=14, gender='女')

# 使用键值对列表创建字典
items = [('color', 'red'), ('size', 'medium'), ('price', 19.99)]
product = dict(items)

# 创建一个字典
student = {
    'name': '小明',
    'age': 15,
    'gender': '男',
    'grades': [85, 92, 78]
}

# 通过键访问值
print(student['name']) # 输出: 小明
print(student['age']) # 输出: 15

# 尝试访问不存在的键（会引发错误）
# print(student['score']) # KeyError: 'score'

# 使用get()方法安全地访问值，不存在则返回默认值
print(student.get('score', 0)) # 输出: 0
print(student.get('name', '未知')) # 输出: 小明

# 获取所有键
print(student.keys()) # 输出类似: dict_keys(['name', 'age', 'gender', 'grades'])
print(list(student.keys())) # 转换为列表: ['name', 'age', 'gender', 'grades']

# 获取所有值
print(student.values()) # 输出类似: dict_values(['小明', 15, '男', [85, 92, 78]])
print(list(student.values())) # 转换为列表: ['小明', 15, '男', [85, 92, 78]]

# 获取所有键值对
print(student.items()) # 输出类似: dict_items([('name', '小明'), ('age', 15), ('gender', '男'), ('grades', [85, 92, 78])])
print(list(student.items())) # 转换为列表: [('name', '小明'), ('age', 15), ('gender', '男'), ('grades', [85, 92, 78])]

# 检查键是否在字典中
if 'name' in student:
    print("字典中包含name键")
else:
    print("字典中不包含name键")

if 'score' not in student:
    print("字典中不包含score键")

# 创建一个字典
student = {
    'name': '小明',
    'age': 15,
    'gender': '男'
}
print("原始字典: ", student)

# 添加新的键值对
student['grades'] = [85, 92, 78]
student['class'] = '初一(1)班'
print("添加键值对后: ", student)

# 更新已有键的值
student['age'] = 16
student['grades'] = [90, 95, 85]
print("更新后: ", student)

# 使用update()方法添加/更新多个键值对
student.update({
    'height': 170,
    'weight': 55,
    'name': '小明同学' # 更新已有键
})
print("使用update()后: ", student)

# 使用del语句删除键值对
del student['weight']
print("删除weight后: ", student)

# 使用pop()方法删除指定键，并返回对应的值
class_value = student.pop('class')
print("删除的class值: ", class_value)
print("删除class后: ", student)

# 尝试删除不存在的键（会引发错误）
# del student['score'] # KeyError: 'score'

# 使用pop()方法安全地删除可能不存在的键
score_value = student.pop('score', None) # 如果不存在，返回None
print("score值: ", score_value)

# 清空字典
student.clear()
print("清空后: ", student) # 输出: {}

# 创建一个字典
student = {
    'name': '小明',
    'age': 15,
    'grades': {'math': 85, 'english': 92, 'chinese': 78}
}

# copy()方法创建浅拷贝
student_copy = student.copy()
print("拷贝的字典: ", student_copy)

# fromkeys()方法创建新字典
keys = ['a', 'b', 'c']
default_dict = dict.fromkeys(keys, 0)
print("fromkeys创建的字典: ", default_dict) # 输出: {'a': 0, 'b': 0, 'c': 0}

# popitem()方法删除并返回最后插入的键值对
last_item = student.popitem()
print("删除的键值对: ", last_item) # 输出类似: ('grades', {'math': 85, 'english': 92, 'chinese': 78})
print("删除后: ", student) # 输出: {'name': '小明', 'age': 15}

# setdefault()方法
gender = student.setdefault('gender', '男') # 键不存在，添加并返回默认值
print("gender值: ", gender)
print("添加gender后: ", student)

name = student.setdefault('name', '未知') # 键存在，返回已有值
print("name值: ", name)

# 创建一个字典
student = {
    'name': '小明',
    'age': 15,
    'gender': '男',
    'grades': {'math': 85, 'english': 92, 'chinese': 78}
}

# 遍历字典的键
print("字典的键: ")
for key in student:
    print(key)

# 或者明确使用keys()方法
for key in student.keys():
    print(key)

# 遍历字典的值
print("\n字典的值: ")
for value in student.values():
    print(value)

# 遍历字典的键值对
print("\n字典的键值对: ")
for key, value in student.items():
    print(f"{key}: {value}")

# 遍历嵌套字典
print("\n成绩详情: ")
for subject, score in student['grades'].items():
    print(f"{subject}: {score}")

# 创建一个班级字典，存储多个学生的信息
class_info = {
    'class_name': '初一(1)班',
    'teacher': '张老师',
    'students': {
        's001': {
            'name': '小明',
            'age': 15,
            'gender': '男',
            'grades': {'math': 85, 'english': 92, 'chinese': 78}
        },
        's002': {
            'name': '小红',
            'age': 14,
            'gender': '女',
            'grades': {'math': 90, 'english': 88, 'chinese': 95}
        },
        's003': {
            'name': '小刚',
            'age': 15,
            'gender': '男',
            'grades': {'math': 76, 'english': 85, 'chinese': 89}
        }
    }
}

# 添加新学生
class_info['students']['s004'] = {
    'name': '小丽',
    'age': 14,
    'gender': '女',
    'grades': {'math': 92, 'english': 90, 'chinese': 88}
}
print("添加新学生后，班级共有", len(class_info['students']), "名学生")

# 查询特定学生信息
student_id = 's002'
if student_id in class_info['students']:
    student = class_info['students'][student_id]
    print(f"学号: {student_id}")
    print(f"姓名: {student['name']}")
    print(f"年龄: {student['age']}")
    print(f"性别: {student['gender']}")
    print(f"成绩: {student['grades']}")

# 更新学生信息
class_info['students']['s001']['age'] = 16
class_info['students']['s001']['grades']['math'] = 90
print(f"更新后，小明的年龄: {class_info['students']['s001']['age']}")
print(f"更新后，小明的数学成绩: {class_info['students']['s001']['grades']['math']}")

# 计算各科平均分
total_math = 0
total_english = 0
total_chinese = 0
num_students = len(class_info['students'])

for student in class_info['students'].values():
    total_math += student['grades']['math']
    total_english += student['grades']['english']
    total_chinese += student['grades']['chinese']

avg_math = total_math / num_students
avg_english = total_english / num_students
avg_chinese = total_chinese / num_students

print("\n班级平均分：")
print(f"数学: {avg_math:.1f}")
print(f"英语: {avg_english:.1f}")
print(f"语文: {avg_chinese:.1f}")

# 找出各科最高分和对应的学生
max_math = -1
max_math_student = ""

for student_id, student in class_info['students'].items():
    if student['grades']['math'] > max_math:
        max_math = student['grades']['math']
        max_math_student = student['name']

print(f"\n数学最高分是{max_math_student}的{max_math}分")