higher_or_lower.py input bug

[ldilley]

If you input a non-integer (letter or word) during the number guess loop, the higher_or_lower.py program terminates with the sample output below.

Welcome to higher or lower! Please type easy, hard, or quit. easy
Try to guess the number I give you! 66
Your guess is a little too low, I dont think you will be beating me any time soon.
Try to guess the number I give you! quit
Traceback (most recent call last):
  File "higher_or_lower.py", line 62, in <module>
    start_game()
  File "higher_or_lower.py", line 33, in start_game
    difficulty_level_easy()
  File "higher_or_lower.py", line 17, in difficulty_level_easy
    guess = int(raw_input('Try to guess the number I give you! '))
ValueError: invalid literal for int() with base 10: 'quit'