code: def is_valid(self, value):
          ''' Whether the value passes validation
  
          Args:
              value (obj) : the value to validate against this property type
  
          Returns:
              True if valid, False otherwise
  
          '''
          try:
              if validation_on():
                  self.validate(value, False)
          except ValueError:
              return False
          else:
              return Truf is_valid(self, value):
          ''' Whether the value passes validation
  
          Args:
              value (obj) : the value to validate against this property type
  
          Returns:
              True if valid, False otherwise
  
          '''
          try:
              if validation_on():
                  self.validate(value, False)
          except ValueError:
              return False
          else:
              return True
docs: Whether the value passes validation
  
          Args:
              value (obj) : the value to validate against this property type
  
          Returns:
              True if valid, False otherwise