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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_source(link):
 """ Return source of the `link` whether it is filename or url. Args: link (str):
 Filename or URL. Returns: str: Content. Raises: UserWarning: When the `link` couldn't be resolved. """

    if link.startswith("http://") or link.startswith("https://"):
        down = httpkie.Downloader()
        return down.download(link)

    if os.path.exists(link):
        with open(link) as f:
            return f.read()

    raise UserWarning("html: '%s' is neither URL or data!" % link)