code: def normalize_value(self, value, transform=True):
          
          if transform:
              value = self.transform_value(value)
          try:
              return float(value)
          except (ValueError, TypeError):
              if self.raise_if_not_float:
                  raise ValueError('Invalid value %s for field %s.%s' % (
                      value, self.model.__name__, self.field.name
                  ))
              return 0
docs: Prepare the given value to be stored in the index
  
          For the parameters, see BaseIndex.normalize_value
  
          Raises
          ------
          ValueError
              If ``raise_if_not_float`` is True and the value cannot
              be casted to a float.