Python字典(dict)操作

python# 创建空字典empty_dict = {}print(empty_dict, type(empty_dict)) # 输出：{} <class 'dict'># 创建带初始键值对的字典（键为字符串、数字，值为不同类型）student = {"name": "张三","age": 20,"score": [90, 85, 95],"is_pass": True}print(student) # 输出：{'name': '张三', 'age': 20, 'score': [90, 85, 95], 'is_pass': True}

python# 方式2.1：通过关键字参数创建fruit = dict(apple=5, banana=3, orange=4)print(fruit) # 输出：{'apple': 5, 'banana': 3, 'orange': 4}# 方式2.2：通过可迭代对象（如列表、元组）创建（元素需为二元组）color = dict([("red", "#FF0000"), ("green", "#00FF00"), ("blue", "#0000FF")])print(color) # 输出：{'red': '#FF0000', 'green': '#00FF00', 'blue': '#0000FF'}

python# 从列表推导生成字典（键为1-5的数字，值为键的平方）square_dict = {x: x*x for x in range(1, 6)}print(square_dict) # 输出：{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

python# 所有键的默认值为Nonekeys = ["a", "b", "c"]default_dict = dict.fromkeys(keys)print(default_dict) # 输出：{'a': None, 'b': None, 'c': None}# 所有键的默认值指定为0count_dict = dict.fromkeys(keys, 0)print(count_dict) # 输出：{'a': 0, 'b': 0, 'c': 0}

pythonstudent = {"name": "张三", "age": 20, "score": [90, 85, 95]}# 访问存在的键print(student["name"]) # 输出：张三print(student["score"][1]) # 访问值为列表的元素，输出：85# 访问不存在的键（会报错KeyError）# print(student["gender"]) # 报错：KeyError: 'gender'

pythonstudent = {"name": "张三", "age": 20}# 访问存在的键print(student.get("name")) # 输出：张三# 访问不存在的键，返回默认值print(student.get("gender")) # 输出：Noneprint(student.get("gender", "未知")) # 自定义默认值，输出：未知

pythonstudent = {"name": "张三", "age": 20}# 修改已存在的键student["age"] = 21print(student) # 输出：{'name': '张三', 'age': 21}# 添加新的键值对student["gender"] = "男"student["address"] = "北京"print(student) # 输出：{'name': '张三', 'age': 21, 'gender': '男', 'address': '北京'}

pythonstudent = {"name": "张三", "age": 20}# 传入字典批量修改/添加update_info = {"age": 21, "gender": "男", "score": 90}student.update(update_info)print(student) # 输出：{'name': '张三', 'age': 21, 'gender': '男', 'score': 90}# 传入二元组列表批量添加student.update([("address", "北京"), ("class", "大一")])print(student) # 输出：{'name': '张三', 'age': 21, 'gender': '男', 'score': 90, 'address': '北京', 'class': '大一'}

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}# 删除指定键值对del student["gender"]print(student) # 输出：{'name': '张三', 'age': 20}# 删除整个字典（删除后字典对象不存在，再访问会报错）del student# print(student) # 报错：NameError: name 'student' is not defined

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}# 删除存在的键，返回对应值age = student.pop("age")print(age) # 输出：20print(student) # 输出：{'name': '张三', 'gender': '男'}# 删除不存在的键，指定默认值score = student.pop("score", 0)print(score) # 输出：0# 删除不存在的键，不指定默认值（报错）# student.pop("score") # 报错：KeyError: 'score'

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}# 删除最后插入的键值对（gender）last_item = student.popitem()print(last_item) # 输出：('gender', '男')print(student) # 输出：{'name': '张三', 'age': 20}

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}# 清空字典student.clear()print(student) # 输出：{}（字典对象仍存在，只是无元素）

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}# 方式1：默认遍历键for key in student:print(key) # 输出：name、age、gender（顺序与插入一致）# 方式2：用keys()方法（明确遍历键，更易读）for key in student.keys():print(key) # 输出结果同上

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}for value in student.values():print(value) # 输出：张三、20、男

pythonstudent = {"name": "张三", "age": 20, "gender": "男"}for key, value in student.items():print(f"{key}: {value}")# 输出：# name: 张三# age: 20# gender: 男

python# 生成键为字母a-e，值为字母大写的字典upper_dict = {chr(97+i): chr(65+i) for i in range(5)}print(upper_dict) # 输出：{'a': 'A', 'b': 'B', 'c': 'C', 'd': 'D', 'e': 'E'}

python# 生成键为1-10的偶数，值为键的平方的字典even_square = {x: x*x for x in range(1, 11) if x % 2 == 0}print(even_square) # 输出：{2: 4, 4: 16, 6: 36, 8: 64, 10: 100}

pythonkeys = ["name", "age", "gender"]values = ["李四", 22, "女"]# 用zip()函数将两个列表配对，再推导成字典student = {k: v for k, v in zip(keys, values)}print(student) # 输出：{'name': '李四', 'age': 22, 'gender': '女'}

pythonstudent = {"name": "张三", "age": 20}# 获取所有键，转换为列表（可迭代对象需转换才能用索引）keys = list(student.keys())print(keys) # 输出：['name', 'age']# 获取所有值，转换为列表values = list(student.values())print(values) # 输出：['张三', 20]# 获取所有键值对，转换为列表items = list(student.items())print(items) # 输出：[('name', '张三'), ('age', 20)]

python# 1. 引用赋值（关联）dict1 = {"a": 1, "b": [2, 3]}dict2 = dict1dict2["a"] = 10dict2["b"].append(4)print(dict1) # 输出：{'a': 10, 'b': [2, 3, 4]}（dict1被修改）# 2. 浅拷贝（表层独立，深层可变类型仍关联）dict3 = dict1.copy()dict3["a"] = 20dict3["b"].append(5)print(dict1) # 输出：{'a': 10, 'b': [2, 3, 4, 5]}（dict1的b列表仍被修改）print(dict3) # 输出：{'a': 20, 'b': [2, 3, 4, 5]}（dict3的a独立）

pythonstudent = {"name": "张三", "age": 20}# 键存在，返回对应值name = student.setdefault("name", "未知")print(name) # 输出：张三print(student) # 无变化：{'name': '张三', 'age': 20}# 键不存在，添加键值对并返回默认值gender = student.setdefault("gender", "未知")print(gender) # 输出：未知print(student) # 输出：{'name': '张三', 'age': 20, 'gender': '未知'}

python# 存储多个学生信息（字典嵌套列表）students = [{"name": "张三", "age": 20, "score": 90},{"name": "李四", "age": 21, "score": 85},{"name": "王五", "age": 20, "score": 95}]# 遍历获取所有学生姓名for s in students:print(s["name"]) # 输出：张三、李四、王五

python# 统计列表中元素出现的次数fruits = ["apple", "banana", "apple", "orange", "banana", "apple"]count = {}for fruit in fruits:# 若元素已存在，计数+1；否则添加元素，计数=1count[fruit] = count.get(fruit, 0) + 1print(count) # 输出：{'apple': 3, 'banana': 2, 'orange': 1}

python# 存储程序配置参数config = {"host": "localhost","port": 8080,"timeout": 30,"debug": True}# 读取配置print(f"连接地址：{config['host']}:{config['port']}") # 输出：连接地址：localhost:8080