import pymongo
c = pymongo.Connection()
coll = c[u'x\u0000'].test
coll.create_index([('x',1)])

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/pymongo/collection.py", line 715, in create_index
    safe=True)
  File "/usr/lib/python2.7/dist-packages/pymongo/collection.py", line 312, in insert
    continue_on_error, self.__uuid_subtype), safe)
  File "/usr/lib/python2.7/dist-packages/pymongo/connection.py", line 822, in _send_message
    return self.__check_response_to_last_error(response)
  File "/usr/lib/python2.7/dist-packages/pymongo/connection.py", line 772, in __check_response_to_last_error
    raise OperationFailure(error["err"], error["code"])
pymongo.errors.OperationFailure: Invalid BSONObj size: 1937339182 (0x2E737973) first element: em.indexes: ?type=116