Find and replace in a file with regular expression

[Matimus]

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)