py re whole file

#!/usr/bin/python3

import re
import sys
#import pdb


def main():
    #pdb.set_trace()
    pattern = re.compile(r"\s*((ALTER_ME_IN_THE_NEW_FILE.*),.*\);)");
    replacement = r"#ifdef F1\n" \
                  "\1\n" \
                  "#else\n" \
                  "\2);\n" \
                  "#endif"
    for num_file, file_name in enumerate(sys.argv[1:], 1):
        print("Starting the change for file: %s" % file_name)
        with open(file_name, "r+") as fhandle:
            orig = fhandle.read()
            repl, changed = re.subn(pattern, replacement, orig)
            if changed:
                fhandle.seek(0)
                fhandle.write(repl)
        print("Finished the change for file: %s" % file_name)
        print("DONE for %d number of files" % num_file)


if __name__ == '__main__':
    main()