Python切换器无法访问

Question

I'm trying to make a simple dictionary mapping but I'm getting an error stating that switcher is unreachable.

def option_select(option):
    switcher = {
        1: "Option One",
        2: "Option Two",
        3: "Option Three",
        4: "Option Four",
        0: sys.exit()
    }
    return switcher.get(option, "Invalid choice")


print("Please select an option:")
print("1: Add a new student.")
print("2: Delete an existing student.")
print("3: List all students.")
print("4: Search for a student.")
print("0: Exit")
optionChoice = int(input("Selection: "))

option_select(optionChoice)

Answer 1

The definition of switcher will execute sys.exit() and your program will end.

Your use of switcher is not a switch statement; it is a dictionary, in which you map the key 0 to the return value of sys.exit() . In order to determine this value and create the dictionary, sys.exit() is executed. sys.exit() exits your program.

The easiest fix is just to deal with exit separately:

def option_select(option):
    if option==0:
        sys.exit()
    switcher = {
        1: "Option One",
        2: "Option Two",
        3: "Option Three",
        4: "Option Four",
    }
    return switcher.get(option, "Invalid choice")

Or you could write your switcher so that each value is callable:

switcher = {
    1: add_student,
    2: delete_student,
    3: list_students,
    4: search_students,
    0: sys.exit,
}

and define the values as functions, and then you can call the result you get from the dictionary to do whatever it is supposed to do.

Eg

switcher[option]()