Google Python Exercise List 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 list exercises

# A. match_ends
# Given a list of strings, return the count of the number of strings where the string length is 2 or more 
# and the first and last chars of the string are the same.
# Note: python does not have a ++ operator, but += works.
def match_ends(words):
  count = 0
  for word in words:
    if len(word) >= 2 and word[0].lower() == word[-1].lower(): count+=1
  return count

# B. front_x
# Given a list of strings, return a list with the strings in sorted order, except group all the strings that begin with 'x' first.
# e.g. ['mix', 'xyz', 'apple', 'xanadu', 'aardvark'] yields ['xanadu', 'xyz', 'aardvark', 'apple', 'mix']
# Hint: this can be done by making 2 lists and sorting each of them before combining them.
def front_x(words):
  words.sort()
  index = 0
  for word in words:
    if word.startswith('x'):
      index = words.index(word)
      break
  return words[index:] + words[:index]

# C. sort_last
# Given a list of non-empty tuples, return a list sorted in increasing order by the last element in each tuple.
# e.g. [(1, 7), (1, 3), (3, 4, 5), (2, 2)] yields [(2, 2), (1, 3), (3, 4, 5), (1, 7)]
# Hint: use a custom key= function to extract the last element form each tuple.
def sort_last(tuples):
  # +++your code here+++
  return sorted(tuples, key=sort_last_value)

## Write a little function that takes a touple, and returns its last value.
def sort_last_value(t):
  return t[-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))

# Calls the above functions with interesting inputs.
def main():
  print 'match_ends'
  test(match_ends(['aba', 'xyz', 'aa', 'x', 'bbb']), 3)
  test(match_ends(['', 'x', 'xy', 'xyx', 'xx']), 2)
  test(match_ends(['aaa', 'be', 'abc', 'hello']), 1)

print '\nfront_x'
  test(front_x(['bbb', 'ccc', 'axx', 'xzz', 'xaa']),['xaa', 'xzz', 'axx', 'bbb', 'ccc'])
  test(front_x(['ccc', 'bbb', 'aaa', 'xcc', 'xaa']),['xaa', 'xcc', 'aaa', 'bbb', 'ccc'])
  test(front_x(['mix', 'xyz', 'apple', 'xanadu', 'aardvark']),['xanadu', 'xyz', 'aardvark', 'apple', 'mix'])

print '\nsort_last'
  test(sort_last([(1, 3), (3, 2), (2, 1)]),[(2, 1), (3, 2), (1, 3)])
  test(sort_last([(2, 3), (1, 2), (3, 1)]),[(3, 1), (1, 2), (2, 3)])
  test(sort_last([(1, 7), (1, 3), (3, 4, 5), (2, 2)]),[(2, 2), (1, 3), (3, 4, 5), (1, 7)])

if __name__ == '__main__':
  main()

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