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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 build_url(base_url, path):
 """ prepend url with base_url unless it's already an absolute URL """

    if absolute_http_url_regexp.match(path):
        return path
    elif base_url:
        return "{}/{}".format(base_url.rstrip("/"), path.lstrip("/"))
    else:
        raise ParamsError("base url missed!")