Safe write acknowledgement (getLastError) fails on MongoDB 2.1.x when authentication is enabled.

>>> import pymongo

>>> c = pymongo.Connection()

>>> c.foo.authenticate('foo', 'pass')

True

>>> c.foo.foo.insert({'foo': 'bar'})

ObjectId('4ffb5678fba5225a5c58b7ff')

>>> c.foo.foo.find_one()

{u'_id': ObjectId('4ffb5678fba5225a5c58b7ff'), u'foo': u'bar'}

>>> c.foo.foo.insert({'foo': 'bim'}, safe=True)

Traceback (most recent call last):

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

  File "pymongo/collection.py", line 306, in insert

    continue_on_error, self.__uuid_subtype), safe)

  File "pymongo/connection.py", line 742, in _send_message

    rv = self.__check_response_to_last_error(response)

  File "pymongo/connection.py", line 678, in __check_response_to_last_error

    helpers._check_command_response(error, self.disconnect)

  File "pymongo/helpers.py", line 129, in _check_command_response

    raise OperationFailure(msg % response["errmsg"])

pymongo.errors.OperationFailure: need to login

>>> for doc in c.foo.foo.find():

...     doc

... 

{u'_id': ObjectId('4ffb5678fba5225a5c58b7ff'), u'foo': u'bar'}

{u'_id': ObjectId('4ffb5687fba5225a5c58b800'), u'foo': u'bim'}