强制用户在 Python 中只输入 Y 或 N

Question

I'm new in programming and my first assessment is creating a program that asks a few questions to the user. The first question requires the user to answer Y or N and I would like to force the user to only do it, by keep asking them the same question until the user type Y or N, without accepting any other letter or number or symbols. If the answer in N, then the user is asked another question (which is apparently working for me) and so on.

I am trying to use while loop and now I'm lost:

print("Phase vaccine rollout (PVR) v1.0")
print("==========================")

phase1a = input("Are you a quarantine and border worker,\n\
prioritised frontline healthcare worker, or\n\
an aged care/disability care staff member or resident (Y/N)?: ")

while phase1a.upper() == "Y" or "N":

 if phase1a.upper() == "Y":
     print()
     print("Vaccines will be made available to you in Phase 1a")
     print()
     exit()

 elif phase1a.upper() == "N":
     print("__________________________")
     phase1b = input("Are you a health care worker, or\n\
a critical or high risk worker (including defence,\n\
police, fire, emergency services and meat processing (Y/N)?: ")
     continue

 else:
     break

# --- and from here I will continue with the phase1b...

Thank you!

Answer 1

Instead of while phase1a.upper() == "Y" or "N": , you could write:

while phase1a.upper() != "Y" and phase1a.upper() != "N":
  print("Invalid input. Please enter "Y" or "N".)
  phase1a = input("Are you a quarantine and border worker,\n\
  prioritised frontline healthcare worker, or\n\
  an aged care/disability care staff member or resident (Y/N)?: ")

You will have to restructure your if statement a bit but hopefully this shows you the idea. This will force the user to keep entering input until he/she enters "Y" or "N".

Answer 2

Using a while True loop will do the trick....

print("Phase vaccine rollout (PVR) v1.0")
print("==========================")

while True:
 phase1a = input("Are you a quarantine and border worker,\n\
prioritised frontline healthcare worker, or\n\
an aged care/disability care staff member or resident (Y/N)?: ")
 if phase1a.upper() == "Y":
     print()
     print("Vaccines will be made available to you in Phase 1a")
     print()
     exit()

 elif phase1a.upper() == "N":
     print("__________________________")
     phase1b = input("Are you a health care worker, or\n\
a critical or high risk worker (including defence,\n\
police, fire, emergency services and meat processing (Y/N)?: ")
     exit()
 else:
     continue

# --- and from here I will continue with the phase1b...

Answer 3

We will be using while True that will end with a else statement which will ask for the user to repeat their input if it is not Y/N. Also to note: You will have to add the result if the user inputs N.

print("Phase vaccine rollout (PVR) v1.0")
print("==========================")

phase1a = input("Are you a quarantine and border worker,\n\
prioritised frontline healthcare worker, or\n\
an aged care/disability care staff member or resident (Y/N)?: ")

while  True:

    if phase1a.upper() == "Y":
    
        print("\nVaccines will be made available to you in Phase 1a\n")
   
        exit()

    elif phase1a.upper() == "N":
        print("__________________________")
        phase1b = input("Are you a health care worker, or\n\
        a critical or high risk worker (including defence,\n\
        police, fire, emergency services and meat processing (Y/N)?: ")
        break

   else:
       phase1a = input("\nAre you a quarantine and border worker,\n\
       prioritised frontline healthcare worker, or\n\
       an aged care/disability care staff member or resident (Y/N)?: ")