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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(*args, **kwargs) -> str: """ Return a valid url. """

    resource_url = API_RESOURCES_URLS
    for key in args:
        resource_url = resource_url[key]

    if kwargs:
        resource_url = resource_url.format(**kwargs)

    return urljoin(URL, resource_url)