python regular expression replacing part of a matched string

Question

i got an string that might look like this

"myFunc('element','node','elementVersion','ext',12,0,0)"

i'm currently checking for validity using, which works fine

myFunc\((.+?)\,(.+?)\,(.+?)\,(.+?)\,(.+?)\,(.+?)\,(.+?)\)

now i'd like to replace whatever string is at the 3rd parameter. unfortunately i cant just use a stringreplace on whatever sub-string on the 3rd position since the same 'sub-string' could be anywhere else in that string.

with this and a re.findall,

myFunc\(.+?\,.+?\,(.+?)\,.+?\,.+?\,.+?\,.+?\)

i was able to get the contents of the substring on the 3rd position, but re.sub does not replace the string it just returns me the string i want to replace with :/

here's my code

myRe = re.compile(r"myFunc\(.+?\,.+?\,(.+?)\,.+?\,.+?\,.+?\,.+?\)")
val =   "myFunc('element','node','elementVersion','ext',12,0,0)"

print myRe.findall(val)
print myRe.sub("noVersion",val)

any idea what i've missed ?

thanks! Seb

Answer 1

In re.sub, you need to specify a substitution for the whole matching string. That means that you need to repeat the parts that you don't want to replace. This works:

myRe = re.compile(r"(myFunc\(.+?\,.+?\,)(.+?)(\,.+?\,.+?\,.+?\,.+?\))")
print myRe.sub(r'\1"noversion"\3', val)