Can't use mongos for secondary reads in Sharded mode

>>> from pymongo import MongoClient

>>> client = MongoClient('mongodb://localhost:1031,localhost:1032')

>>> # wait a moment...

...

>>> client.is_mongos

True

>>> client.nodes

frozenset([('localhost', 1031), ('localhost', 1032)])

>>> client.database.collection.find_one() is None

True

>>> from pymongo import ReadPreference

>>> client.get_database('database', 

...    read_preference=ReadPreference.SECONDARY).collection.find_one()

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

  File "pymongo/collection.py", line 772, in find_one

    for result in cursor.limit(-1):

  File "pymongo/cursor.py", line 977, in __next__

    if len(self.__data) or self._refresh():

  File "pymongo/cursor.py", line 914, in _refresh

    self.__codec_options))

  File "pymongo/cursor.py", line 822, in __send_message

    **kwargs)

  File "pymongo/mongo_client.py", line 804, in _send_message_with_response

    server = topology.select_server(selector)

  File "pymongo/topology.py", line 113, in select_server

    server_selection_timeout))

  File "pymongo/topology.py", line 93, in select_servers

    self._error_message(selector))

pymongo.errors.ServerSelectionTimeoutError: No mongoses match selector "Secondary(tag_sets=None)"