Sort a list of items interactively

interactive_sort.py

yes_letters = set('yt')
no_letters = set('nf')

def read_bool(prompt):
    '''Read a boolean value from standard input.'''
    answer = None
    while answer not in yes_letters and answer not in no_letters:
        answer = raw_input(prompt).strip()[0].lower()
    return answer in yes_letters

def input_cmp(this, that):
    '''Ask the user to choose between two items.

    Return -1 if the first item was chosen, otherwise 1.
    '''
    this_better_than_that = read_bool('Is %s better than %s? (y/n)' % (this, that))
    if this_better_than_that:
        return -1 # This comes *before* that
    else:
        return 1 # This comes *after* that

def main():
    # Feel free to add your own
    languages = '''C C++ C# Python Ruby
                   Java Scala Haskell OCaml Forth
                   Scheme Ada BASIC D Go'''.split()
    languages.sort(cmp=input_cmp)
    print '\n'.join(languages)

if __name__ == '__main__':
    main()