code: def _parse_deadline(deadline):
          
          if '-' in deadline and len(deadline) == 10:
              return deadline
  
          if '.' in deadline and len(deadline) == 10:  # russian format dd.mm.yyyy to yyyy-mm-dd
              dmy = deadline.split('.')
              if len(dmy) == 3 and all(v is not None for v in dmy):
                  return '-'.join(reversed(dmy))
  
          raise exceptions.RumetrUnparsableDeadline()
docs: Translate deadline date from human-acceptable format to the machine-acceptable