code: def update_headers(src_tree):
      
      print("src tree", src_tree)
      for root, dirs, files in os.walk(src_tree):
          py_files = fnmatch.filter(files, "*.py")
          for f in py_files:
              print("checking", f)
              p = os.path.join(root, f)
              with open(p) as fh:
                  contents = fh.read()
              if suffix in contents:
                  continue
              print("Adding license header to %s" % p)
              with open(p, 'w') as fh:
                  fh.write(
                      '%s%s%s' % (header, suffix, contents))
docs: Main.