old_contents: import copy
  import collections
  import weakref
  
  class Result(object):
      def __init__(self, satness, model, backend_model=None):
          self.sat = satness
          self.model = model
          self.backend_model = backend_model
          self.eval_cache = { }
          self.min_cache = { }
          self.max_cache = { }
          self.resolve_cache = collections.defaultdict(weakref.WeakKeyDictionary)
  
      def branch(self):
          r = Result(self.sat, copy.copy(self.model), backend_model=self.backend_model)
          r.eval_cache = dict(self.eval_cache)
          r.min_cache = dict(self.min_cache)
          r.max_cache = dict(self.max_cache)
  
      def __getstate__(self):
          return ( self.sat, self.model, self.eval_cache, self.min_cache, self.max_cache )
  
      def __setstate__(self, state):
          ( self.sat, self.model, self.eval_cache, self.min_cache, self.max_cache ) = state
          self.backend_model = None
  
new_contents: import copy
  import collections
  import weakref
  
  class Result(object):
      def __init__(self, satness, model, backend_model=None):
          self.sat = satness
          self.model = model
          self.backend_model = backend_model
          self.eval_cache = { }
          self.min_cache = { }
          self.max_cache = { }
          self.resolve_cache = collections.defaultdict(weakref.WeakKeyDictionary)
  
      def branch(self):
          r = Result(self.sat, copy.copy(self.model), backend_model=self.backend_model)
          r.eval_cache = dict(self.eval_cache)
          r.min_cache = dict(self.min_cache)
          r.max_cache = dict(self.max_cache)
  
      def __getstate__(self):
          return ( self.sat, self.model, self.eval_cache, self.min_cache, self.max_cache )
  
      def __setstate__(self, state):
          ( self.sat, self.model, self.eval_cache, self.min_cache, self.max_cache ) = state
          self.resolve_cache = collections.defaultdict(weakref.WeakKeyDictionary)
          self.backend_model = None
  
subject: create empty resolution cache on Result deserialization