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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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