How to repeat the input until a special condition is met in Python?

I need to take integer inputs from the user and add them to a set. The number of integers is unknown. The input process will end when the user input is "Done".

Here is my code:

s = set()
print('Please type the number, when you are done please type "Done":')
while True:
    try:
        a = int(input())
        s.add(a)
    except:
        if a == "Done":
            break
        else:
            print('Integer only, please re-type:')
            continue
print(s)

But it didn't work as intended.

My idea is simple. If the user types an integer then it's fine, just add to set s. If they type a string (which int(input() is wrong), then it will go down to except, if the string is "Done", then break the while True loop, if it isn't then ask the user to re-type and continue the loop.

Here is the error if I type a string first and if I type normally:

I tried to use a simple if-else statement at the start but it causes traceback right at int(input()).

Solution

When the exception happens, a remains unset. Try this instead.

s = set()
# Notice also correct quoting
print("Please type the number, when you're done please type 'Done':")
while True:
    a = input()
    try:
        n = int(a)
        s.add(n)
    # Avoid blanket except
    except ValueError:
        if a == "Done":
            break
        else:
            print('Integer only, please re-type:')
            continue
print(s)