python dict 字典常用方法 (java-map)

def test_dict():
    """
    测试字典的基本操作
    """
    var20 = {"name": "Alice", "age": 30, "city": "New York"}
    print("var20:", var20)

    # 添加元素
    var20["job"] = "Engineer"
    print("添加 job:", var20)

    # 删除元素
    del var20["age"]
    print("删除 age:", var20)

    var20.update({"country": "USA"})  # 更新或添加元素
    print("更新或添加 country:", var20)

    pop_val = var20.pop("city")  # 删除并返回指定键的值
    print("删除并返回 city 的值:", pop_val)

    all_keys = var20.keys()
    print("所有键:", all_keys)

    all_values = var20.values()
    print("所有值:", all_values)

    empty_person = dict.fromkeys(["name", "age", "city"])  # 创建一个空字典，指定键
    print('创建一个空字典，指定键:', empty_person)

    popitem_dict = var20.popitem()  # 删除并返回字典中的最后一个键值对
    print("删除并返回最后一个键值对:", popitem_dict)

    var20.setdefault("name1", "Default Name")  # 如果键不存在，则设置默认值
    print("设置默认值 name:", var20)

    # 获取值
    name = var20.get("name")
    print("获取 name:", name)

    # 检查键是否存在
    has_city = "city" in var20
    print("是否有 city 键:", has_city)

    # 遍历字典
    for key, value in var20.items():
        print(f"{key}: {value}")

    # 字典推导式  key = x  ,value = x的2次方  并且满足 x % 2 == 0
    squared = {x: x ** 2 for x in range(5) if x % 2 == 0}  # 生成一个字典，键为0-4的偶数，值为其平方
    print(squared)

结果

var20: {‘name’: ‘Alice’, ‘age’: 30, ‘city’: ‘New York’}
添加 job: {‘name’: ‘Alice’, ‘age’: 30, ‘city’: ‘New York’, ‘job’: ‘Engineer’}
删除 age: {‘name’: ‘Alice’, ‘city’: ‘New York’, ‘job’: ‘Engineer’}
更新或添加 country: {‘name’: ‘Alice’, ‘city’: ‘New York’, ‘job’: ‘Engineer’, ‘country’: ‘USA’}
删除并返回 city 的值: New York
所有键: dict_keys([‘name’, ‘job’, ‘country’])
所有值: dict_values([‘Alice’, ‘Engineer’, ‘USA’])
创建一个空字典，指定键: {‘name’: None, ‘age’: None, ‘city’: None}
删除并返回最后一个键值对: (‘country’, ‘USA’)
设置默认值 name: {‘name’: ‘Alice’, ‘job’: ‘Engineer’, ‘name1’: ‘Default Name’}
获取 name: Alice
是否有 city 键: False
name: Alice
job: Engineer
name1: Default Name
{0: 0, 2: 4, 4: 16}