Google String Exercise One

#!/usr/bin/python -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/

# Basic string exercises

# A. donuts
# Given an int count of a number of donuts, return a string of the form 'Number of donuts: <count>', where <count> is the number passed in. 
# However, if the count is 10 or more, then use the word 'many' instead of the actual count.
def donuts(count):
  result = 'many'
  if count < 10 :
    result = str(count)
  return 'Number of donuts: X'.replace('X',result)

# B. both_ends
# Given a string s, return a string made of the first 2 and the last 2 chars of the original string, 
# However, if the string length is less than 2, return instead the empty string.
def both_ends(s):
  if len(s) < 2:
    return '';
  return s[:2] + s[-2:]

# C. fix_start
# Given a string s, return a string where all occurences of its first char have been changed to '*', 
# except do not change the first char itself.
# Assume that the string is length 1 or more.
def fix_start(s):
  return s[:1] + s[1:].replace(s[:1],'*')

# D. MixUp
# Given strings a and b, return a single string with a and b separated by a space '<a> <b>', 
# except swap the first 2 chars of each string.
# Assume a and b are length 2 or more.
def mix_up(a, b):
  return b[:2] + a[2:] + ' ' + a[:2] + b[2:]

# Provided simple 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))

# Provided main() calls the above functions with interesting inputs,
# using test() to check if each result is correct or not.
def main():
  print 'donuts'
  # Each line calls donuts, compares its result to the expected for that call.
  test(donuts(4), 'Number of donuts: 4')
  test(donuts(9), 'Number of donuts: 9')
  test(donuts(10), 'Number of donuts: many')
  test(donuts(99), 'Number of donuts: many')

print
  print 'both_ends'
  test(both_ends('spring'), 'spng')
  test(both_ends('Hello'), 'Helo')
  test(both_ends('a'), '')
  test(both_ends('xyz'), 'xyyz')

print
  print 'fix_start'
  test(fix_start('babble'), 'ba**le')
  test(fix_start('aardvark'), 'a*rdv*rk')
  test(fix_start('google'), 'goo*le')
  test(fix_start('donut'), 'donut')

print
  print 'mix_up'
  test(mix_up('mix', 'pod'), 'pox mid')
  test(mix_up('dog', 'dinner'), 'dig donner')
  test(mix_up('gnash', 'sport'), 'spash gnort')
  test(mix_up('pezzy', 'firm'), 'fizzy perm')

# Standard boilerplate to call the main() function.
if __name__ == '__main__':
  main()

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