Here is a general format. You can either use re.sub or re.match, based on your requirement. Below is a general pattern for opening a file and doing it:

import re

input_file = open("input.h", "r")
output_file = open("output.h.h", "w")
br = 0
ot = 0

for line in input_file:
    match_br = re.match(r'\s*#define .*_BR (0x[a-zA-Z_0-9]{8})', line) # Should be your regular expression
    match_ot = re.match(r'\s*#define (.*)_OT (0x[a-zA-Z_0-9]+)', line) # Second regular expression

if match_br:
    br = match_br.group(1)
    # Do something

elif match_ot:
    ot = match_ot.group(2)
    # Do your replacement

else:
    output_file.write(line)

You can use Notepad++ with Version >= 6.0. Since then it does support PCRE Regex.

You can then use your regex a(.+?)a and replace with $1

Thanks Jimilan for your remarks. I fixed my code, and now it`s working:

        base_regex   = re.compile(.*test_mode.*base_sw=(\S*))
        target_regex = re.compile(.*test_mode.*target_sw=(\S*))

        for file in self.upgrade_cases_files_list:

            file_handle = open(file, 'r')
            file_string = file_handle.read()
            file_handle.close()

            base_version_result   = base_regex.search(file_string)
            target_version_result = target_regex.search(file_string)

            if base_version_result is not None:
                current_base_version = base_version_result.group(1)
            else:
                raise Exception("Could not detect base version in the following file: -> %s \n" % (file))

            if target_version_result is not None:
                current_target_version = target_version_result.group(1)
            else:
                raise Exception("Could not detect target version in the following file: -> %s \n" % (file))

            file_string = file_string.replace(current_base_version, self.base_version)
            file_string = file_string.replace(current_target_version, self.target_version)

            file_handle = open(file, 'w')
            file_handle.write(file_string)
            file_handle.close()

If your file is short (or even not extremely long), you can use the following snippet to replace text in place:

# Replace variables in file
with open('path/to/in-out-file', 'r+') as f:
    content = f.read()
    f.seek(0)
    f.truncate()
    f.write(content.replace('replace this', 'with this'))