字典

字典的创建

# 大括号直接创建
dict1 = {"张三": 20, "李四": 30}
print(dict1)

# 使用dict函数创建
dict1 = dict(name="zhangsan", age=18)
print(dict1)

# 创建空字典
dict1 = {}
print(dict1)

字典元素的获取

dict1 = {"张三": 20, "李四": 30}

# 使用[]获取，没有key则返回抛KeyError
print(dict1["张三"])  # 20
# print(dict1["王五"]) # KeyError: '张四'

# 使用get方法，没有key则返回None
print(dict1.get("张三"))  # 20
print(dict1.get("王五"))  # None
print(dict1.get("赵六", 60))  # 60；查不到，返回默认值

字典的增删改查

# 字典的 key 判断
dict1 = {"张三": 20, "李四": 30}
print("张三" in dict1)  # True
print("张三" not in dict1)  # False

# 删除指定键值对
dict1 = {"张三": 20, "李四": 30}
del dict1["张三"]
print(dict1)  # {'李四': 30}

# 清空字典所有元素
dict1 = {"张三": 20, "李四": 30}
dict1.clear()
print(dict1)  # {}

# 新增字典元素，修改字典元素
dict1 = {"张三": 20, "李四": 30}
dict1["王五"] = 60
print(dict1)  # {}
dict1["王五"] = 80
print(dict1)  # {}

# 获取字典所有的key
dict1 = {"张三": 20, "李四": 30}
keys = dict1.keys()
print(keys)
print(type(keys))
print(list(keys))

# 获取字典所有的value
dict1 = {"张三": 20, "李四": 30}
values = dict1.values()
print(values)
print(type(values))
print(list(values))

# 获取字典所有的键值对
dict1 = {"张三": 20, "李四": 30}
items = dict1.items()
print(items)
print(type(items))
print(list(items))

字典元素遍历

dict1 = {"张三": 20, "李四": 30}
for item in dict1:
    print(item, dict1[item], dict1.get(item))

字典的 key 必须是不可变对象

# 字典的特点
# key不重复，value可以重复
# 字典元素是无序的
# 字典的key必须是不可变对象
list1 = [100, 200]
dict1 = {"key1": 10, "key2": 20}
# dict1 = {list1: 30} # TypeError: unhashable type: 'list'
print(dict1)

字典生成式

# 字典生成式；使用zip函数
key1 = ["k1", "k2", "k3"]
value1 = [10, 20, 30]
dict1 = {my_key: my_value for my_key, my_value in zip(key1, value1)}
print(dict1)