#!/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 # 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 list2.py. # 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): # +++your code here+++ count = 0 for word in words : if len(word) >=2 and word[0] == word[-1] : 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): # +++your code here+++ xgroup = [] othgroup = [] for word in words : if word[0] == 'x' : xgroup.append(word) else : othgroup.append(word) othgroup.sort() xgroup.sort() xgroup.extend(othgroup) return xgroup # 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+++ tuples.sort(key=last) return tuples # Extract the last element from a tuple -- used for custom sorting below. def last(a): return a[-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 print 'front_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 print 'sort_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()