code: def add_path_part(url, regex=PATH_PART):
      
      formatter = string.Formatter()
      url_var_template = "(?P<{var_name}>{regex})"
  
      for part in formatter.parse(url):
          string_part, var_name, _, _ = part
          if string_part:
              yield string_part
          if var_name:
              yield url_var_template.format(var_name=var_name, regex=regex)
docs: replace the variables in a url template with regex named groups
      :param url: string of a url template
      :param regex: regex of the named group
      :returns: regex