def is_valid_input(letter_guessed):
    """
	param letter_guessed: a string from the user
	type letter_guessed: str
	return: false or true
	"""
    if (len(letter_guess) == 1) and letter_guess.isalpha():
        return True
    elif len(letter_guess) > 1:
        return False
    elif not(letter_guess.isalpha()):
        return False

def main():
    letter_guess = input("Guess a letter: ")
	is_valid_input(letter_guess)

if __name__ == "__main__":
    main()