docs: def parse_diff_filenames(diff_files):
          """Parse the output of filenames_diff_cmd."""
          # ?   .gitignore
          # M  0.txt
          files = []
          for line in diff_files.splitlines():
              line = line.strip()
              fn = re.findall('[^ ]+\s+(.*.py)', line)
              if fn and not line.startswith('?'):
                  files.append(fn[0])
          return files