Ok so i have this piece of code:

def findNReplaceRegExp(file_name, regexp, replaceString, verbose=True, confirmationNeeded=True):
   Replaces the oldString with the replaceString in the file given,
   returns the number of replaces
   
    # initialize local variables
    cregexp = re.compile(regexp, re.MULTILINE | re.DOTALL)
    somethingReplaced = True
    ocurrences = 0
    isAborted = False

    # open file for read
    file_in = open(file_name,  r )
    file_in_string = file_in.read()
    file_in.close()

    while somethingReplaced:
        somethingReplaced = False
        # if the regexp is found
        if cregexp.search(file_in_string):
            # make the substitution
            replaced_text = re.sub(regexp, replaceString, file_in_string)
            if verbose == True:
                # calculate the segment of text in which the resolution will be done

                # print the old string and the new string
                print  -   + file_in_string
                print  +   + replaced_text
                if confirmationNeeded:
                    # ask user if this should be done
                    question = raw_input( Accept changes? [Yes (Y), No (n), Abort (a)]  )
                    question = string.lower(question)
                    if question ==  a :
                        isAborted = True
                        print "Aborted"
                        break
                    elif question ==  n :
                        pass
                    else:
                        file_in_string = replaced_text
                        somethingReplaced = True
                        ocurrences = ocurrences + 1
            else:
                file_in_string = replaced_text
                somethingReplaced = True
                ocurrences = ocurrences + 1

    # if some text was replaced, overwrite the original file
    if ocurrences > 0 and not isAborted:
        # open the file for overwritting
        file_out = open(file_name,  w )
        file_out.write(file_in_string)
        file_out.close()
        if verbose: print "File " + file_name + " written"

And this file

CMC_SRS T10-24400: DKU Data Supply: SN Time Break-In Area
CMC_SRS T10-24401: DKU Data Supply: SN Transponder Enable Area
CMC_SRS T10-24402: DKU Data Supply: SN Adjust Master Slave Area
CMC_SRS T10-24403: DKU Data Supply: SN ATEC Area
CMC_SRS T10-24404: DKU Data Supply: SN PTEC Area
CMC_SRS T10-25449: DKU Data Supply: SN Self Init Area
CMC_SRS T10-24545: DKU Data Supply: SN Time Area
CMC_SRS T10-4017: RFI display update
CMC_SRS T10-6711: Radio Interface to PLS Equipment
CMC_SRS T10-21077: Safety Requirements: Limit FM Power

When i call the procedure with this file and these parameters: regexp=24403.*24404 replace=TESTSTRING

i get a coincidence (it matches and questions what to do) but when its time to replace nothing happens... Whats wrong??