>>> 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)"