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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 download_if_not_exists(url: str, filename: str, skip_cert_verify: bool = True, mkdir: bool = True) -> None: """ Downloads a URL to a file, unless the file already exists. """

    if os.path.isfile(filename):
        log.info("No need to download, already have: {}", filename)
        return
    if mkdir:
        directory, basename = os.path.split(os.path.abspath(filename))
        mkdir_p(directory)
    download(url=url,
             filename=filename,
             skip_cert_verify=skip_cert_verify)