1.代码如下

代码如下（示例）：

d = {1: 'a', 2: 'b', 3: 'c'}
a = int(input("请输入键："))

if a not in list(d.keys()):
    print('用户的键不存在')
else:
    print('字典中%d键对应的值为%s' % (a, d.get(a)))

2.运行结果

D:\Python代码\Scripts\python.exe C:/Users/Lenovo/PycharmProjects/pythonFirstStart/实验/demo7.py
请输入键：1
字典中1键对应的值为a

Process finished with exit code 0






D:\Python代码\Scripts\python.exe C:/Users/Lenovo/PycharmProjects/pythonFirstStart/实验/demo7.py
请输入键：5
用户的键不存在

Process finished with exit code 0