python技术—字典

1. 创建字典

字典特点：

• 符号为大括号
• 数据为键值对形式出现
• 各个键值对之间用逗号隔开

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
dict2 = {}      #空字典
dict3 = dict()  #空字典

注意：⼀般称冒号前⾯的为键(key)，简称k；冒号后⾯的为值(value)，简称v。

2. 字典常见操作

2.1 添加

字典元素添加写法：字典[key] = 值，注意如果key存在，则修改这个key对应的值，如果key不存在，则新增此键值对

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)
dict1['work'] = "coder"
print("2:",dict1)

结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: {'name': 'Tom', 'age': 20, 'gender': '男', 'work': 'coder'}

2.2 删除

del()/del:删除字典或删除字典中指定键值对

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)
dict1['work'] = "coder"
print("2:",dict1)
del dict1["name"]
print("3:",dict1)
del dict1
print("4:",dict1)
结果：
Traceback (most recent call last):
  File "D:/PyProm/dictTest.py", line 12, in <module>
    print("4:",dict1)
NameError: name 'dict1' is not defined
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: {'name': 'Tom', 'age': 20, 'gender': '男', 'work': 'coder'}
3: {'age': 20, 'gender': '男', 'work': 'coder'}

clear():清空字典，删除字典中所有的元素

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)
dict1['work'] = "coder"
print("2:",dict1)
dict1.clear()
print("3:",dict1)
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: {'name': 'Tom', 'age': 20, 'gender': '男', 'work': 'coder'}
3: {}

pop():删除拥有指定键的元素

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)
dict1['work'] = "coder"
print("2:",dict1)
dict1.pop("name")
print("3:",dict1)
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: {'name': 'Tom', 'age': 20, 'gender': '男', 'work': 'coder'}
3: {'age': 20, 'gender': '男', 'work': 'coder'}

popitem():从字典中删除最后一个键值对

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)
dict1['work'] = "coder"
print("2:",dict1)
dict1.popitem()
print("3:",dict1)
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: {'name': 'Tom', 'age': 20, 'gender': '男', 'work': 'coder'}
3: {'name': 'Tom', 'age': 20, 'gender': '男'}

2.3 修改

写法： 字典序列 [key] = 值

注意：如果key存在则修改这个key对应的值 ；如果key不存在则新增此键值对。

2.4 查找

• key值查找          

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)

print("2:",dict1["name"])
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: Tom

• get()

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)

print("2:",dict1["name"])
print("3:",dict1.get("name"))
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: Tom
3: Tom

• keys()

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)

print("2:",dict1["name"])
print("3:",dict1.get("name"))
print("4:",dict1.keys())
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: Tom
3: Tom
4: dict_keys(['name', 'age', 'gender'])

• values()

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)

print("2:",dict1["name"])
print("3:",dict1.get("name"))
print("4:",dict1.values())
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: Tom
3: Tom
4: dict_values(['Tom', 20, '男'])

• items()

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
print("1:",dict1)

print("2:",dict1["name"])
print("3:",dict1.get("name"))
print("4:",dict1.items())
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: Tom
3: Tom
4: dict_items([('name', 'Tom'), ('age', 20), ('gender', '男')])

2.5 更新

update() 方法向字典插入指定的项目。 这个指定项目可以是字典或可迭代对象。

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
dict2 = {"hobby":"running","diet":"chicken","subject":"math"}
print("1:",dict1)
print("2:",dict2)
print("3:",dict1.update(dict2))
print("4:",dict1)
结果：
1: {'name': 'Tom', 'age': 20, 'gender': '男'}
2: {'hobby': 'running', 'diet': 'chicken', 'subject': 'math'}
3: None
4: {'name': 'Tom', 'age': 20, 'gender': '男', 'hobby': 'running', 'diet': 'chicken', 'subject': 'math'}

3. 字典遍历

3.1 遍历字典的key

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
for key in dict1.keys():
    print(key)
结果：
name
age
gender

3.2 遍历字典的value

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
for key in dict1.keys():
    print("1:",key)
for value in dict1.values():
    print("2:",value)
结果：
1: name
1: age
1: gender
2: Tom
2: 20
2: 男

3.3 遍历字典的元素

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
for key in dict1.keys():
    print("1:",key)
for value in dict1.values():
    print("2:",value)
for item in dict1.items():
    print("3:",item)
结果：
1: name
1: age
1: gender
2: Tom
2: 20
2: 男
3: ('name', 'Tom')
3: ('age', 20)
3: ('gender', '男')

3.4 遍历字典的键值对

dict1 = {"name": "Tom", "age": 20, "gender": "男"} #有数据字典
# for key in dict1.keys():
#     print("1:",key)
# for value in dict1.values():
#     print("2:",value)
# for item in dict1.items():
#     print("3:",item)
for key, value in dict1.items():
    print("4:",f'{key} = {value}')
结果：
4: name = Tom
4: age = 20
4: gender = 男