The following will continuously prompt the user for input until they enter exactly one character.
userInput = '' while len(userInput) != 1: userInput = raw_input(':') guessInLower = userInput.lower()
This does the same, but also informs them of the one character limit before prompting again for input
while True: userInput = raw_input(':') if len(userInput) == 1: break print 'Please enter only one character' guessInLower = userInput.lower()
It looks like you are expecting only letters. If that is the case you can expand this further to require that:
import string while True: userInput = raw_input(':') if len(userInput) == 1: if userInput in string.letters: break print 'Please enter only letters' else: print 'Please enter only one character' guessInLower = userInput.lower()