old_contents: from skypyblue.models import Strength
  
  class Variable:
    def __init__(self, name, value, system = None, walk_strength = Strength.WEAKEST):
      self.name = name
      self.value = value
      self.constraints = []
      self.determined_by = None
      self.walk_strength = walk_strength
      self.mark = None
      self.valid = True
      self.system = system
      self.stay_constraint = None
  
    def get_value(self):
      return self.value
  
    def set_value(self, value):
      self.value = value
      if self.system is not None:
        self.system.variable_changed(self)
  
    def remove_constraint(self,constraint):
        self.constraints=[cn for cn in self.constraints if cn!=constraint]
  
    def add_constraint(self, constraint):
      self.constraints.append(constraint)
  
    def stay(self, strength=Strength.WEAK):
      if self.stay_constraint is not None:
        self.cd.remove_constraint(self.stay_constraint)
  
      self.stay_constraint = self.system.add_stay_constraint(self,strength)
  
    def removeStayConstraint(self):
      if self.stay_constraint is not None:
        self.system.remove_constraint(self.stay_constraint)
        self.stay_constraint = None
  
  
    def __repr__(self):
      return "<Variable '%s', value: %s>" % (self.name, self.value)
  
  
new_contents: from skypyblue.models import Strength
  
  class Variable:
    def __init__(self, name, value, system = None, walk_strength = Strength.WEAKEST):
      self.name = name
      self.value = value
      self.constraints = []
      self.determined_by = None
      self.walk_strength = walk_strength
      self.mark = None
      self.valid = True
      self.system = system
      self.stay_constraint = None
  
    def get_value(self):
      return self.value
  
    def set_value(self, value):
      self.value = value
      if self.system is not None:
        self.system.variable_changed(self)
  
    def remove_constraint(self,constraint):
        self.constraints=[cn for cn in self.constraints if cn!=constraint]
  
    def add_constraint(self, constraint):
      self.constraints.append(constraint)
  
    def stay(self, strength=Strength.WEAK):
      if self.stay_constraint is not None:
        self.system.remove_constraint(self.stay_constraint)
  
      self.stay_constraint = self.system.add_stay_constraint(self,strength)
  
    def removeStayConstraint(self):
      if self.stay_constraint is not None:
        self.system.remove_constraint(self.stay_constraint)
        self.stay_constraint = None
  
  
    def __repr__(self):
      return "<Variable '%s', value: %s>" % (self.name, self.value)
  
  
subject: fix typo