string1.py

#!/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
# Fill in the code for the functions below. main() is already set up
# to call the functions with a few different inputs,
# printing 'OK' when each function is correct.
# The starter code for each function includes a 'return'
# which is just a placeholder for your code.
# It's ok if you do not complete all the functions, and there
# are some additional functions to try in string2.py.


# 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.
# So donuts(5) returns 'Number of donuts: 5'
# and donuts(23) returns 'Number of donuts: many'
def donuts(count):
  s = ""
  if count == 10 or count > 10:
      s = "Number of donuts: many"
  else:
      s = "Number of donuts: " + str(count)
  return s

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


# 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.
# e.g. 'babble' yields 'ba**le'
# Assume that the string is length 1 or more.
# Hint: s.replace(stra, strb) returns a version of string s
# where all instances of stra have been replaced by strb.
def fix_start(s):
    first_letter = s[0]
    s = s[1:].replace(first_letter, "*")
    s = first_letter + s
    return s

# 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.
# e.g.
#   'mix', pod' -> 'pox mid'
#   'dog', 'dinner' -> 'dig donner'
# Assume a and b are length 2 or more.
def mix_up(a, b):
  s = b[:2] + a[2:] + " " + a[:2] + b[2:]
  return s


# 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()