human
Solve the following python programming problem given the following code:
def get_push_for_request(self, requestid) : 
    pushid = [None] 
    def on_select_return(success, db_results) : 
        assert success 
        (_, pushid [0]) = db_results.fetchone () 
first_pushcontent_query = db.push_pushcontents.select ((db.push_pushcontents.c.request == requestid)) 
    db.execute_cb (<MASK>, on_select_return) 
    return pushid [0] 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: first_pushcontent_query, pushid, self, on_select_return, requestid
assistant
#Here is a proper replacement for <MASK>.
first_pushcontent_query