The re module is used for regular expressions. Something like this should work (untested):
import fileinput, string, sys, re fileQuery = "Text.txt" sourceText = '''SOURCE''' replaceText = '''REPLACE''' def replace(fileName, sourceText, replaceText): file = open(fileName, "r") text = file.read() #Reads the file and assigns the value to a variable file.close() #Closes the file (read session) file = open(fileName, "w") file.write(re.sub(sourceText, replaceText,text)) file.close() #Closes the file (write session) print "All went well, the modifications are done" replacemachine(fileQuery, sourceText, replaceText) -- http://mail.python.org/mailman/listinfo/python-list