import penndraw as pd
letter = "s"
still_guessing = True
while still_guessing:
    if pd.has_next_key_typed():
        guess = pd.next_key_typed()
        if guess == letter:
            still_guessing = False
        else:
            pd.clear()
            pd.text(0.5, 0.5, f"Not {guess}, try again!")
    pd.advance()

pd.clear(pd.GREEN)
pd.text(0.5, 0.5, f"Hurray! {letter} is right.")
pd.run()