code: def discover_files(base_path, sub_path='', ext='', trim_base_path=False):
      
      file_list = []
      for root, dirs, files in walk(path.join(base_path, sub_path)):
          if trim_base_path:
              root = path.relpath(root, base_path)
          file_list.extend([path.join(root, file_name)
                            for file_name in files
                            if file_name.endswith(ext)])
      return sorted(file_list)
docs: Discovers all files with certain extension in given paths.