#!/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):
  # test if string ends in 'ing'
  if s[-3:] == 'ing':
    # append 'ly'
    return s + 'ly'
  # otherwise test if string length is at least 3
  elif len(s) >= 3:
    # append 'ing'
    return s + 'ing'
  # otherwise test if string length is less than 3
  elif len(s) < 3:
    # return string unchanged
    return 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):
  # try to find the index of 'bad'
  try:
    bad_i = s.index('bad')
  # the 'bad' substring is not present
  except ValueError:
    # set index of 'bad' equal to zero
    bad_i = 0
  # try to find the index of 'not'
  try:
  # not 'not' substring is not present
    not_i = s.index('not')
  except ValueError:
    # set index of 'not' to zero
    not_i = 0
  # test if 'not' comes before 'bad'
  if (bad_i > not_i):
    # positive test - replace the 'not'...'bad' substring with 'good'
    return s[0:not_i] + 'good' + s[bad_i+3:]
  # negative test
  else:
    # return the string unchanged
    return 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):
  # test if a is odd
  a_odd = len(a)%2
  # test if b is odd
  b_odd = len(b)%2
  # if a is odd set offset so extra char goes in the front half
  if a_odd:
    split_a = (len(a)/2)+1
  # a is even - split down the middle
  else:
    split_a = len(a)/2
  # if b is odd set offset so extra char goes in the front half
  if b_odd:
    split_b = (len(b)/2)+1
  # b is even - split down the middle
  else:
    split_b = len(b)/2
  # set string variables accordingly using slice syntax
  a_front = a[:split_a]
  a_back = a[split_a:]
  b_front = b[:split_b]
  b_back = b[split_b:]
  # build the return string
  return a_front + b_front + a_back + b_back


# 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()