text: # Copyright (c) 2006-2016  Andrey Golovizin
  #
  # Permission is hereby granted, free of charge, to any person obtaining
  # a copy of this software and associated documentation files (the
  # "Software"), to deal in the Software without restriction, including
  # without limitation the rights to use, copy, modify, merge, publish,
  # distribute, sublicense, and/or sell copies of the Software, and to
  # permit persons to whom the Software is furnished to do so, subject to
  # the following conditions:
  #
  # The above copyright notice and this permission notice shall be
  # included in all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  # EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  # MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  # IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
  # CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  # TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  # SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  
  from pybtex.plugin import Plugin
  
  
  class BaseSortingStyle(Plugin):
      def sorting_key(self, entry):
          raise NotImplementedError
  
      def sort(self, entries):
          entry_dict = dict(
              (self.sorting_key(entry), entry)
              for entry in entries
          )
          sorted_keys = sorted(entry_dict)
          sorted_entries = [entry_dict[key] for key in sorted_keys]
          return sorted_entries
  