docs: def _findroot(self, x):
          """Internal MIBDict function used to find a partial OID"""
          if x.startswith("."):
              x = x[1:]
          if not x.endswith("."):
              x += "."
          max = 0
          root = "."
          root_key = ""
          for k in six.iterkeys(self):
              if x.startswith(k + "."):
                  if max < len(k):
                      max = len(k)
                      root = self[k]
                      root_key = k
          return root, root_key, x[max:-1]