code: def evaluate_preconditions(self, request):
          
          if request.method.upper() in self.precondition_map.keys():
              required_headers = self.precondition_map.get(request.method.upper(), [])
              # check the required headers
              for header in required_headers:
                  if not request.META.get(prepare_header_name(header)):
                      # raise an error for each header that does not match
                      logger.warning('Precondition required: %s', request.path,
                                     extra={
                                         'status_code': status.HTTP_428_PRECONDITION_REQUIRED,
                                         'request': request
                                     }
                                     )
                      # raise an RFC 6585 compliant exception
                      raise PreconditionRequiredException(detail='Precondition required. This "%s" request '
                                                                 'is required to be conditional. '
                                                                 'Try again using "%s".' % (request.method, header)
                                                          )
          return True
docs: Evaluate whether the precondition for the request is met.