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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 add_download_filename(response: HttpResponse, filename: str) -> None: """ Adds a ``Content-Disposition`` header to the HTTP response to say that there is an attachment with the specified filename. """

    # https://docs.djangoproject.com/en/1.9/howto/outputting-csv/
    add_http_headers_for_attachment(response)
    response['Content-Disposition'] = 'attachment; filename="{}"'.format(
        filename)