Just enough of a mongoserver to handle a mongo shell connecting.

mongoserver.py

#!/usr/bin/env python

"""
A sample Mongo server that handles enough of the commands to connect
with the mongo shell.

Requires: https://github.com/chergert/mongo-async-python-driver
"""

from collections      import OrderedDict
from twisted.internet import defer, protocol, reactor
from txmongo.protocol import MongoProtocol, Reply

class MyMongoServer(MongoProtocol):
    def handle_QUERY(self, request):
        if request.collection.endswith('.$cmd'):
            doc = request.query.decode(as_class=OrderedDict)
            if doc.keys()[0] == 'ismaster':
                ret = {'ismaster': True, 'maxBsonSize': 16 * 1024 * 1024, 'ok': 1}
                reply = Reply(response_to=request.request_id, documents=[ret])
                self.send(reply)
            elif doc.keys()[0] == 'whatsmyuri':
                peer = self.transport.getPeer()
                ret = {"you": '%s:%d' % (peer.host, peer.port), "ok": 1}
                reply = Reply(response_to=request.request_id, documents=[ret])
                self.send(reply)
            elif doc.keys()[0] == 'replSetGetStatus':
                ret = {"errmsg": "not running with --replSet", "ok": 0}
                reply = Reply(response_to=request.request_id, documents=[ret])
                self.send(reply)

if __name__ == '__main__':
    factory = protocol.Factory()
    factory.protocol = MyMongoServer
    reactor.listenTCP(8181, factory)
    reactor.run()