code: def _get_diff(self):
          
          diff = []
          self._create_sot_file()
          diff_out = self._send_command(
              "show diff rollback-patch file {} file {}".format(
                  "sot_file", self.candidate_cfg
              ),
              raw_text=True,
          )
          try:
              diff_out = (
                  diff_out.split("Generating Rollback Patch")[1]
                  .replace("Rollback Patch is Empty", "")
                  .strip()
              )
              for line in diff_out.splitlines():
                  if line:
                      if line[0].strip() != "!" and line[0].strip() != ".":
                          diff.append(line.rstrip(" "))
          except (AttributeError, KeyError):
              raise ReplaceConfigException(
                  "Could not calculate diff. It's possible the given file doesn't exist."
              )
          return "\n".join(diff)
docs: Get a diff between running config and a proposed file.