def _in_download(self, url):
        self._debug('Provider', '_in_download', 'No callback supplied.')
validate against an existing storable
dataset/ETHPy150Open JakeWharton/py-videodownloader/videodownloader/providers/__init__.py/Provider._in_download--crossover with--dataset/ETHPy150Open pydata/pandas/pandas/io/pytables.py/Fixed.validate