nodes: 0, module; 1, function_definition; 2, function_name:get_http_headers; 3, parameters; 4, block; 5, default_parameter; 6, default_parameter; 7, default_parameter; 8, expression_statement; 9, if_statement; 10, if_statement; 11, if_statement; 12, expression_statement; 13, expression_statement; 14, return_statement; 15, identifier:user_agent; 16, None; 17, identifier:referer; 18, None; 19, identifier:accept_language; 20, None; 21, comment:"""
      Update the default requests HTTP headers with OSMnx info.
  
      Parameters
      ----------
      user_agent : str
          the user agent string, if None will set with OSMnx default
      referer : str
          the referer string, if None will set with OSMnx default
      accept_language : str
          make accept-language explicit e.g. for consistent nominatim result sorting
  
      Returns
      -------
      headers : dict
      """; 22, comparison_operator:user_agent is None; 23, block; 24, comparison_operator:referer is None; 25, block; 26, comparison_operator:accept_language is None; 27, block; 28, assignment; 29, call; 30, identifier:headers; 31, identifier:user_agent; 32, None; 33, expression_statement; 34, identifier:referer; 35, None; 36, expression_statement; 37, identifier:accept_language; 38, None; 39, expression_statement; 40, identifier:headers; 41, call; 42, attribute; 43, argument_list; 44, assignment; 45, assignment; 46, assignment; 47, attribute; 48, argument_list; 49, identifier:headers; 50, identifier:update; 51, dictionary; 52, identifier:user_agent; 53, attribute; 54, identifier:referer; 55, attribute; 56, identifier:accept_language; 57, attribute; 58, attribute; 59, identifier:default_headers; 60, pair; 61, pair; 62, pair; 63, identifier:settings; 64, identifier:default_user_agent; 65, identifier:settings; 66, identifier:default_referer; 67, identifier:settings; 68, identifier:default_accept_language; 69, identifier:requests; 70, identifier:utils; 71, string; 72, identifier:user_agent; 73, string; 74, identifier:referer; 75, string; 76, identifier:accept_language; 77, string_content:User-Agent; 78, string_content:referer; 79, string_content:Accept-Language
code: def get_http_headers(user_agent=None, referer=None, accept_language=None):
      """
      Update the default requests HTTP headers with OSMnx info.
  
      Parameters
      ----------
      user_agent : str
          the user agent string, if None will set with OSMnx default
      referer : str
          the referer string, if None will set with OSMnx default
      accept_language : str
          make accept-language explicit e.g. for consistent nominatim result sorting
  
      Returns
      -------
      headers : dict
      """
  
      if user_agent is None:
          user_agent = settings.default_user_agent
      if referer is None:
          referer = settings.default_referer
      if accept_language is None:
          accept_language = settings.default_accept_language
  
      headers = requests.utils.default_headers()
      headers.update({'User-Agent': user_agent, 'referer': referer, 'Accept-Language': accept_language})
      return headers