code: def get_config_files():
          
          # Configure the config parser
          apps_dir = os.path.join(os.path.dirname(os.path.realpath(__file__)),
                                  APPS_DIR)
          custom_apps_dir = os.path.join(os.environ['HOME'], CUSTOM_APPS_DIR)
  
          # List of stock application config files
          config_files = set()
  
          # Temp list of user added app config file names
          custom_files = set()
  
          # Get the list of custom application config files first
          if os.path.isdir(custom_apps_dir):
              for filename in os.listdir(custom_apps_dir):
                  if filename.endswith('.cfg'):
                      config_files.add(os.path.join(custom_apps_dir,
                                                    filename))
                      # Also add it to the set of custom apps, so that we don't
                      # add the stock config for the same app too
                      custom_files.add(filename)
  
          # Add the default provided app config files, but only if those are not
          # customized, as we don't want to overwrite custom app config.
          for filename in os.listdir(apps_dir):
              if filename.endswith('.cfg') and filename not in custom_files:
                  config_files.add(os.path.join(apps_dir, filename))
  
          return config_files
docs: Return the application configuration files.
  
          Return a list of configuration files describing the apps supported by
          Mackup. The files return are absolute full path to those files.
          e.g. /usr/lib/mackup/applications/bash.cfg
  
          Only one config file per application should be returned, custom config
          having a priority over stock config.
  
          Returns:
              set of strings.