Newbie seeks help on case preserving substitutions

[Nicola Musatti]

Hi,
I have a number of files which contain different variations of the same
string, e.g.

ECBASE
ECBase
ecbase

Which I want to substitute with a different string, while preserving the
original case, e.g.

OWTEST
OWTest
owtest

What I'm currently doing is search for the first string ignoring case,
and substitute the second character by character according to the first
string's case:

for line in inFile.readlines():
    matchRes = re.compile(oldString).search(line)
    if matchRes:
	found = 1
	new = line[:matchRes.start()]
	for i in range(matchRes.start(),matchRes.end()):
	    if line[i] in string.uppercase:
		new = new + string.upper(newString[i-matchRes.start()])
	    else:
		new = new + string.lower(newString[i-matchRes.start()])
	    new = new + line[matchRes.end():]

I was wondering if there's a more compact way to do what I want.

Thanks,
Nicola Musatti