code: def wrann(self, write_fs=False, write_dir=''):
          
          for field in ['record_name', 'extension']:
              if getattr(self, field) is None:
                  raise Exception('Missing required field for writing annotation file: ',field)
  
          present_label_fields = self.get_label_fields()
          if not present_label_fields:
              raise Exception('At least one annotation label field is required to write the annotation: ', ann_label_fields)
  
          # Check the validity of individual fields
          self.check_fields()
  
          # Standardize the format of the custom_labels field
          self.standardize_custom_labels()
  
          # Create the label map used in this annotaion
          self.create_label_map()
  
          # Check the cohesion of fields
          self.check_field_cohesion(present_label_fields)
  
          # Calculate the label_store field if necessary
          if 'label_store' not in present_label_fields:
              self.convert_label_attribute(source_field=present_label_fields[0],
                                           target_field='label_store')
  
          # Write the header file using the specified fields
          self.wr_ann_file(write_fs=write_fs, write_dir=write_dir)
  
          return
docs: Write a WFDB annotation file from this object.
  
          Parameters
          ----------
          write_fs : bool, optional
              Whether to write the `fs` attribute to the file.