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

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