code: def check_ends_with_period(self, definition, docstring):
          
          if docstring:
              summary_line = ast.literal_eval(docstring).strip().split('\n')[0]
              if not summary_line.endswith('.'):
                  return violations.D400(summary_line[-1])
docs: D400: First line should end with a period.
  
          The [first line of a] docstring is a phrase ending in a period.