text: #!/usr/bin/python2.4 -tt
  # Copyright 2010 Google Inc.
  # Licensed under the Apache License, Version 2.0
  # http://www.apache.org/licenses/LICENSE-2.0
  
  # Google's Python Class
  # http://code.google.com/edu/languages/google-python-class/
  
  # Additional basic string exercises
  
  
  # D. verbing
  # Given a string, if its length is at least 3,
  # add 'ing' to its end.
  # Unless it already ends in 'ing', in which case
  # add 'ly' instead.
  # If the string length is less than 3, leave it unchanged.
  # Return the resulting string.
  def verbing(s):
      return s + 'ing' if len(s) >= 3 and s[-3:] != 'ing' else s + 'ly' if s[-3:] == 'ing' else s
  
  
  # E. not_bad
  # Given a string, find the first appearance of the
  # substring 'not' and 'bad'. If the 'bad' follows
  # the 'not', replace the whole 'not'...'bad' substring
  # with 'good'.
  # Return the resulting string.
  # So 'This dinner is not that bad!' yields:
  # This dinner is good!
  def not_bad(s):
      return s[:s.find('not')] + 'good' + s[s.find('bad') + 3 :] if s.find('bad') > s.find('not') else s
  
  
  # F. front_back
  # Consider dividing a string into two halves.
  # If the length is even, the front and back halves are the same length.
  # If the length is odd, we'll say that the extra char goes in the front half.
  # e.g. 'abcde', the front half is 'abc', the back half 'de'.
  # Given 2 strings, a and b, return a string of the form
  #  a-front + b-front + a-back + b-back
  def front_back(a, b):
      def divide(s):
          cut = len(s) // 2 + len(s) % 2
          return s[:cut], s[cut:]
      a = divide(a)
      b = divide(b)
      return a[0] + b[0] + a[1] + b[1]
  
  
  # Simple provided test() function used in main() to print
  # what each function returns vs. what it's supposed to return.
  def test(got, expected):
      if got == expected:
          prefix = ' OK '
      else:
          prefix = '  X '
      print('%s got: %s expected: %s' % (prefix, repr(got), repr(expected)))
  
  
  # main() calls the above functions with interesting inputs,
  # using the above test() to check if the result is correct or not.
  def main():
      print('verbing')
      test(verbing('hail'), 'hailing')
      test(verbing('swiming'), 'swimingly')
      test(verbing('do'), 'do')
  
      print()
      print('not_bad')
      test(not_bad('This movie is not so bad'), 'This movie is good')
      test(not_bad('This dinner is not that bad!'), 'This dinner is good!')
      test(not_bad('This tea is not hot'), 'This tea is not hot')
      test(not_bad("It's bad yet not"), "It's bad yet not")
  
      print()
      print('front_back')
      test(front_back('abcd', 'xy'), 'abxcdy')
      test(front_back('abcde', 'xyz'), 'abcxydez')
      test(front_back('Kitten', 'Donut'), 'KitDontenut')
  
  
  if __name__ == '__main__':
      main()
  