code: def get_collection(self, collection, database_name=None, username=None, password=None):
          
          _db = self.get_database(database_name, username, password)
          return _db[collection]
docs: Get a pymongo collection handle.
  
          :param collection: Name of collection
          :param database_name: (optional) Name of database
          :param username: (optional) Username to login with
          :param password: (optional) Password to login with
          :return: Pymongo collection object