python读取txt文件，查找到指定内容，并做出修改

def modifyip(tfile,sstr,rstr):
    try:
        lines=open(tfile,'r').readlines()
        flen=len(lines)-1
        for i in range(flen):
            if sstr in lines[i]:
                lines[i]=lines[i].replace(sstr,rstr)
        open(tfile,'w').writelines(lines)
        
    except Exception,e:
        print e
        
modifyip('a.txt','a','A')

def modifyip(tfile,sstr,rstr):
try:
lines=open(tfile,'r').readlines()
flen=len(lines)-1
for i in range(flen):
if sstr in lines[i]:
lines[i]=lines[i].replace(sstr,rstr)
open(tfile,'w').writelines(lines)

except Exception,e:
print e

modifyip('a.txt','a','A')