正则搜索内容并自定义替换

#正则搜索内容并自定义替换
#使用自行修改
#没替换成功常见错误
#没找到要替换的字符串
#正则式不对

import re

#1 use number serial to replace
#2 use define word in file to replace
#3 use constent word to replace
replace_methed=3

#input text
sourcefile="D:\\test\\rep.txt"
#output text
destfile="D:\\test\\rep_1.txt"
srcf=open(sourcefile,"r")

#1
reptag=0

#2
f2=open("D:\\test\\gg.txt","r")
replists=f2.readlines()
replists_pos=0

#3 constent string to replace
repstring="example string"

#compile the regex of searching string
myre=re.compile("(\n)",re.I | re.DOTALL | re.MULTILINE)

#source content
content=srcf.read()

#test content
#content="xxxxxasdfa sdfsab sdfklsajfa asdfkdjsflb"


dd=myre.search(content)
newcontent=""
while dd!=None:
    newcontent+=content[:dd.start()]
    for ddi in range(1,len(dd.groups())+1):
        if(ddi==1):
            if(replace_methed==1):
                newcontent+=str(reptag)
                reptag+=1
            elif(replace_methed==2):
                if(replists_pos<len(replists)):
                    if(replists[replists_pos].endswith("\n")):
                        newcontent+=replists[replists_pos][:-1]
                    else:
                        newcontent+=replists[replists_pos]
                    replists_pos+=1
                else:
                    replists_pos=0
                    if(replists[replists_pos].endswith("\n")):
                        newcontent+=replists[replists_pos][:-1]
                    else:
                        newcontent+=replists[replists_pos]
                    replists_pos+=1
            elif(replace_methed==3):
                newcontent+=repstring
                reptag+=1
        else:
            newcontent+=dd.group(ddi)
    content=content[dd.end():]
    dd=myre.search(content)
if(dd==None):
    newcontent+=content
destf=open(destfile,"w")
destf.write(newcontent)
destf.close()
srcf.close()