文件修改

f=open('yesterday','r',encoding='utf-8')

f_new=open('yesterday.bak','w',encoding='utf-8')

for line in f:
    if '当我小的时候' in line:
        line=line.replace('当我小的时候','当zhow小的时候')
    f_new.write(line)
f.close()
f_new.close()