code: def process_header(self, data):
          
          metadata = {
              "datacolumns": data.read_chunk("I"),
              "firstyear": data.read_chunk("I"),
              "lastyear": data.read_chunk("I"),
              "annualsteps": data.read_chunk("I"),
          }
          if metadata["annualsteps"] != 1:
              raise InvalidTemporalResError(
                  "{}: Only annual files can currently be processed".format(self.filepath)
              )
  
          return metadata
docs: Reads the first part of the file to get some essential metadata
  
          # Returns
          return (dict): the metadata in the header