code: def _project_single_observable(self, **kwargs: Dict[str, Any]) -> Hist:
          
          # Help out mypy
          assert isinstance(self.output_attribute_name, str)
  
          # Run the actual projection.
          output_hist, projection_name, projection_name_args, = self._project_observable(
              input_key = "single_observable",
              input_observable = self.observable_to_project_from,
              **kwargs,
          )
          # Store the output.
          output_hist_args = projection_name_args
          output_hist_args.update({  # type: ignore
              "output_hist": output_hist,
              "projection_name": projection_name
          })
  
          # Store the final histogram.
          output_hist = self.output_hist(**output_hist_args)  # type: ignore
  
          # Store the final output hist
          if not hasattr(self.output_observable, self.output_attribute_name):
              raise ValueError(f"Attempted to assign hist to non-existent attribute {self.output_attribute_name} of object {self.output_observable}. Check the attribute name!")
          # Actually store the histogram.
          setattr(self.output_observable, self.output_attribute_name, output_hist)
  
          # Return the observable
          return output_hist
docs: Driver function for projecting and storing a single observable.
  
          Args:
              kwargs (dict): Additional named args to be passed to projection_name(...) and output_key_name(...)
          Returns:
              The projected histogram. The histogram is also stored in the output specified by ``output_observable``.