为什么即使输入是整数，我也会不断收到 TypeError？

Question

I'm coding something for a school project which asks the user for a number between 0-10 and I have no idea why I keep getting a TypeError even though the input is converted to integer using a list. Any help please? I'm doing this on Wing IDE 101.

numbers = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"]
while True:
    num = ''
    while num == '':
        try:
            num = input("Please enter a number: ")
            num = int(num)
        except ValueError:
            if num in numbers:
                num = numbers.index(num)
                num = int(num)
            else:
                print('Invalid input, please enter valid input')
    if num == 0:
        print("Thank you for using this program")
        break
    elif num < 0 or num > 10:
        print("This is an invalid number, please enter a valid number.")
        print()
        continue

Answer 1

I think this the reason:

When your input is not a valid input like "asdf" . It will jump out the inner while loop. Because you inner while loop condition is num == '' while num is "asdf" now.

You should just put num = "" under print('Invalid input, please enter valid input') and your code will work and not raise TypeError anymore.

Complete code below:

numbers = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"]
while True:
    num = ''
    while num == '':
        try:
            num = input("Please enter a number: ")
            num = int(num)
        except ValueError:
            if num in numbers:
                num = numbers.index(num)
                num = int(num)
            else:
                print('Invalid input, please enter valid input')
                num = ""
    if num == 0:
        print("Thank you for using this program")
        break
    elif num < 0 or num > 10:
        print("This is an invalid number, please enter a valid number.")
        print()
        continue

In fact your code could be simpfy to one loop:

numbers = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"]
while True:
    num = input("Please enter a number: ")
    if num in numbers:
        num = numbers.index(num)
    else:
        try:
            num = int(num)
        except ValueError:
            print("Invalid input, please enter valid input")
            continue
    if num == 0:
        print("Thank you for using this program")
        break
    elif num < 0 or num > 10:
        print("This is an invalid number, please enter a valid number.")

Answer 2

What happens to you can happen a lot in dynamic language since the types are resolved on runtime rather on design time, so sometimes it is hard to figure.

First, separate the user_input from the number ( num ) you are evaluating, into 2 different parameters (one for user input string and one for integer) - I know it does not matter on Python, but it is a good practice.

Now your num value will only be assigned on a successful parsing. No need for continue at the end of the loop as well

Code Snippet

numbers = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"]
while True:
    user_input = ''
    num = None  # default invalid value
    while num is None:
        try:
            user_input = input("Please enter a number: ")
            num = int(user_input)
        except ValueError:
            if user_input in numbers:
                num = numbers.index(user_input)
            else:
                print('Invalid input, please enter valid input')
                print()
    if num == 0:
        print("Thank you for using this program")
        break
    elif num < 0 or num > 10:
        print("This is an invalid number, please enter a valid number.")
        print()

Debug Output

Please enter a number: 1
Please enter a number: one
Please enter a number: 11
This is an invalid number, please enter a valid number.

Please enter a number: -1
This is an invalid number, please enter a valid number.

Please enter a number: no numbder
Invalid input, please enter valid input

Please enter a number: 0
Thank you for using this program

Process finished with exit code 0