【python编程从入门到到实践】第六章 字典

1.简单的字典示例

student = {'name': 'zhangsan', 'score': 80}
print(student['name'])
print(student['score'])

2.添加键值对

student['high'] = 180
print(student)

3.定义空字典

• map = {}

4.修改字典值

student = {'name': 'zhangsan', 'score': 80}
student['name'] = 'lisi'
print(student)

5.删除键值对

• 需要指出字典名和键

student = {'name': 'zhangsan', 'score': 80}
del student['name']
print(student)

6.get()

• 当要访问的键可能不存在时，使用get( , )

student = {'name': 'zhangsan', 'score': 80}
tmp = student.get('high', ) # 第二个参数为空默认返回‘None’
print(tmp)
tmp = student.get('high', 'No')
print(tmp)

7.遍历字典

1.遍历键值对

student = {'name': 'zhangsan', 'score': 80}
for key,value in student.items():print(key)print(value)

2. 遍历键

student = {'name': 'zhangsan', 'score': 80}
for key in student.keys(): # keys()可以省略，加上是为了使代码更清晰。print(key)

注意：可以使用keys()检查字典中是否存在指定键。if 'name' not in student.keys():

3. 按特定的顺序遍历键

student = {'zoo': 'tiger', 'name': 'zhangsan', 'score': 80}
for key in sorted(student.keys()):print(key)

4.遍历值（会包含重复）

student = {'lisi': 180, 'zhangsan': 180, 'wangwu': 170}
for high in student.values():print(high)

5. 遍历值（不会包含重复）

student = {'lisi': 180, 'zhangsan': 180, 'wangwu': 170}
for high in set(student.values()): # 使用set可以去重print(high)

8.嵌套

1.字典列表

xiaoming = {'high': 180, 'age': 25, 'weigh': 80}
zhangsan = {'high': 170, 'age': 24, 'weigh': 79}
lisi = {'high': 185, 'age': 26, 'weigh': 85}
student = [xiaoming, zhangsan, lisi]
for i in student:print(i)

2.列表字典

student = {'high': 180, 'name': ['zhangsan', 'lisi','wangwu']}
for i in student['name']:print(i)

3.字典字典

• 分支字典的结构尽量一致，方便循环。