b = {1:'张三', 2:'老王', 3:'王五'}

def select(sid):
    # 判断sid这个id是否是字典的键
    if sid in b:
        return b[sid]   # 根据键取值
    else:
        return None

if __name__ == '__main__':

    print(select(1))
    print(select(2))