old_contents: # Copyright (c) 2013 Leif Johnson <leif@leifjohnson.net>
  #
  # 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.
  
  '''Base classes for simulations.'''
  
  
  class World(object):
      '''World is a small base class for simulation worlds.'''
  
      def needs_reset(self):
          '''Return True iff the world needs to be reset.'''
          return False
  
      def reset(self):
          '''Reset the world state.'''
          pass
  
      def trace(self):
          '''Return a string containing world state for later analysis.'''
          return None
  
      def step(self):
          '''Advance the world simulation by one time step.'''
          raise NotImplementedError
  
new_contents: # Copyright (c) 2013 Leif Johnson <leif@leifjohnson.net>
  #
  # 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.
  
  '''Base classes for simulations.'''
  
  
  class World(object):
      '''World is a small base class for simulation worlds.'''
  
      def needs_reset(self):
          '''Return True iff the world needs to be reset.'''
          return False
  
      def reset(self):
          '''Reset the world state.'''
          pass
  
      def trace(self):
          '''Return a string containing world state for later analysis.'''
          return None
  
      def step(self):
          '''Advance the world simulation by one time step.'''
          raise NotImplementedError
  
      def on_key_press(self, key, keys):
          '''Handle an otherwise-unhandled keypress event.'''
          self.reset()
  
subject: Allow for World to handle key presses.