'Generate book sort key with computed author_sort.
Generate a sort key of computed author_sort, title. Used to look for
author_sort mismatches.
Twiddle included to force series to sort after non-series books.
\'Smith, john Star Wars\'
\'Smith, john ~Star Wars 0001.0000\'
Args:
book (dict): book metadata
Return:
(str): sort key'

def _kf_books_by_author_sorter_author(self, book):

    if (not book['series']):
        key = ('%s    %s' % (self._kf_author_to_author_sort(book['author']), capitalize(book['title_sort'])))
    else:
        index = book['series_index']
        integer = int(index)
        fraction = (index - integer)
        series_index = ('%04d%s' % (integer, str(('%0.4f' % fraction)).lstrip('0')))
        key = ('%s    ~%s    %s' % (self._kf_author_to_author_sort(book['author']), self.generate_sort_title(book['series']), series_index))
    return key
