python 读取大文件

with open('a.txt','r',encoding='utf-8') as f:
    # l=[]
    # for line in f:
    #     # print(len(line))
    #     l.append(len(line))

    g=(len(line) for line in f)
    res=max(g)
    print(res)

    # print(max(len(line) for line in f))