code: def update_one(self, query, doc):
          
          if self.table is None:
              self.build_table()
  
          if u"$set" in doc:
              doc = doc[u"$set"]
  
          allcond = self.parse_query(query)
  
          try:
              result = self.table.update(doc, allcond)
          except:
              # TODO: check table.update result
              # check what pymongo does in that case
              result = None
  
          return UpdateResult(raw_result=result)
docs: Updates one element of the collection
  
          :param query: dictionary representing the mongo query
          :param doc: dictionary representing the item to be updated
          :return: UpdateResult