old_contents: # Copyright (c) 2006, 2007, 2008, 2009, 2010, 2011  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
  
  available_plugins = ('number',)
  
  
  class BaseLabelStyle(Plugin):
      default_plugin = 'number'
  
      def format(self, entry):
          raise NotImplementedError
  
new_contents: # Copyright (c) 2006, 2007, 2008, 2009, 2010, 2011  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
  
  available_plugins = ('number',)
  
  
  class BaseLabelStyle(Plugin):
      default_plugin = 'number'
  
      def get_longest_label(self, formatted_entries):
          #FIXME: determine label width proprely
          return max(formatted_entries, key=lambda entry: len(entry.label)).label
  
      def format(self, entry):
          raise NotImplementedError
  
subject: Add BaseLabelStyle.get_longest_label() method.