def Open(self, urn, aff4_type=None, mode="r"):
    key = self._ObjectKey(urn, mode)

    try:
      obj = self._objects_cache[key]
    except KeyError:
      obj = FACTORY.Open(urn, mode=mode, follow_symlinks=False,
                         token=self._token)
      self._objects_cache[key] = obj

    if (aff4_type is not None and
        not isinstance(obj, AFF4Object.classes[aff4_type])):
      raise InstantiationError(
          "Object %s is of type %s, but required_type is %s" % (
              urn, obj.__class__.__name__, aff4_type))

    return obj
Opens the named object.
dataset/ETHPy150Open google/grr/grr/lib/aff4.py/DeletionPool.Open