打印字典时出现KeyError？

Question

所以我正在尝试编写一个程序，让用户输入课程编号，然后获取该课程的房间、讲师和会议时间信息。如果用户输入的课程未找到/无效，我希望能够打印终止消息，但是当我尝试时，它会出现 KeyError。 我尝试过使用 try/except 语句，但是当我执行代码时会出现 TypeError。

room_dict = {
    "CS101": {
        "Room": "3004"
    },
    "CS102": {
        "Room": "4501"
    },
    "CS103": {
        "Room": "6755"
    },
    "NT110": {
        "Room": "1244"
    },
    "CM241": {
        "Room": "1411"
    },
}


instructor_dict = {
    "CS101": {
        "Instructor": "Haynes"
    },
    "CS102": {
        "Instructor": "Alvarado"
    },
    "CS103": {
        "Instructor": "Rich"
    },
    "NT110": {
        "Instructor": "Burkes"
    },
    "CM241": {
        "Instructor": "Lee"
    },
}


time_dict = {
    "CS101": {
        "Time": "8:00 a.m."
    },
    "CS102": {
        "Time": "9:00 a.m."
    },
    "CS103": {
        "Time": "10:00 a.m."
    },
    "NT110": {
        "Time": "11:00 a.m."
    },
    "CM241": {
        "Time": "1:00 p.m."
    },
}

courses = {"CS101", "CS102", "CS103", "NT110", "CM241"}
dicts = {'Room':room_dict,'Instructor':instructor_dict,'Time': time_dict}

dash_count = 50
dashes = dash_count * "-"

print(f'College Course Locater Program')
print(f'Enter a course number below to get information')
get_course = input(f'Enter a course number: ')
print(dashes)

course_num = get_course
room = room_dict[get_course]
instructor = instructor_dict[get_course]
time = time_dict[get_course]

if course_num in courses:
    print(f'The details for course {get_course} are: ')
    print(f"Room: {room['Room']}")
    print(f"Time: {time['Time']}")
    print(f"Instructor: {instructor['Instructor']}")

其他： print(course_num, '是一个无效的课程编号。')

基本上，我得到的输出是：

College Course Locater Program
Enter a course number below to get information
Enter a course number: CS # where CS is an invalid course number
--------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\Python\Downloads\courseinfo.py", line 75, in <module>
    room = room_dict[get_course]
KeyError: 'CS'

我正在寻找的是：

College Course Locater Program
Enter a course number below to get information
Enter a course number: CS
--------------------------------------------------
(course number) is an invalid course number. # where (course number) is an invalid course number

Answer 1

多个问题：

首先，您检查if get_course == room_dict:。但是room_dict 是整个字典！它永远不会等于您输入的课程编号。

其次，无需循环for item in room_dict.items():。字典中的值应该使用它们的键来访问。所以你会做类似的事情

get_course = input(f'Enter a course number: ')

print(f'The details for course {get_course} are: ')
room = room_dict[get_course]
instructor = instructor_dict[get_course]
time = time_dict[get_course]
print(f"Room: {room['Room']}, Time: {time['Time']}, Instructor: {instructor['Instructor']}")

当然，您需要确保get_course 作为所有这些字典中的键存在。你可以这样做

• Look before you leap 通过检查密钥是否明确存在：if get_course in room_dict: 或，
• 使用 try-except 捕获 KeyError。毕竟是easier to ask for forgiveness than permission

try:
    room = room_dict[get_course]
    instructor = instructor_dict[get_course]
    time = time_dict[get_course]
except KeyError:
    print("Course info not found")

更好的是，您可以重新定义您的字典，以便一个字典包含有关课程的所有信息。

course_info = {
    "CS101": {
        "Room": "3004",
        "Instructor": "Haynes",
        "Time": "8:00 a.m."
    },
    "CS102": {
        "Room": "4501",
       "Instructor": "Alvarado",
       "Time": "9:00 a.m."
    }
# and so on
}

然后简单地做：

get_course = input(f'Enter a course number: ')

try:
    crs = course_info[get_course]
    print(f'The details for course {get_course} are: ')
    print(f"Room: {crs['Room']}, Time: {crs['Time']}, Instructor: {crs['Instructor']}")
except KeyError:
    print(f"Details not found for {get_course}")

Answer 2

下面的代码应该会让你的生活更轻松。

它使用course_name = 'CM241' 仅用于演示目的。

room_dict = {
    "CS101": {
        "Room": "3004"
    },
    "CS102": {
        "Room": "4501"
    },
    "CS103": {
        "Room": "6755"
    },
    "NT110": {
        "Room": "1244"
    },
    "CM241": {
        "Room": "1411"
    },
}


instructor_dict = {
    "CS101": {
        "Instructor": "Haynes"
    },
    "CS102": {
        "Instructor": "Alvarado"
    },
    "CS103": {
        "Instructor": "Rich"
    },
    "NT110": {
        "Instructor": "Burkes"
    },
    "CM241": {
        "Instructor": "Lee"
    },
}


time_dict = {
    "CS101": {
        "Time": "8:00 a.m."
    },
    "CS102": {
        "Time": "9:00 a.m."
    },
    "CS103": {
        "Time": "10:00 a.m."
    },
    "NT110": {
        "Time": "11:00 a.m."
    },
    "CM241": {
        "Time": "1:00 p.m."
    },
}

dicts = {'Time':time_dict,'Room':room_dict,'Instructor': instructor_dict}
course_name = 'CM241'
for k,v in dicts.items():
  print(f'{k} --> {v[course_name][k]}')

输出

Time --> 1:00 p.m.
Room --> 1411
Instructor --> Lee