Script do get all changes that differ from the original base defconfig, ideally to apply the changes to another device config in the future.

defconfig_differ.py

import re, sys

if len(sys.argv) != 3:
    print(f"""Usage: {sys.argv[0]} <base_defconfig> <custom_defconfig>
          
For best results, use savedefconfig generated configs.""")
    exit(1)

cfg_base    = sys.argv[1]
cfg_custom  = sys.argv[2]

def cfg_purify(f):
    lines = f.read().splitlines()
    for i, e in enumerate(lines):
        match = re.search('# ([^\s]+) is not set', e)
        if match:
            config = match.group(1)
            lines[i] = f"{config}=n"
    lines = [ x for x in lines if '#' not in x ]
    return lines

def cfg_diff():
    with open(cfg_base, 'r') as f:
        base_lines = cfg_purify(f)
    
    with open(cfg_custom, 'r') as f:
        custom_lines = cfg_purify(f)
    
    diff_lines = []
    for line in custom_lines:
        if line not in base_lines:
            diff_lines.append(line)
    
    for line in diff_lines:
        print(line)
    
cfg_diff()