def __init__(self, outdir, clean=False, file_extension='png'):
        self.outdir = outdir
        self.mkdir(self.outdir, clean=clean)
        self.file_extension = file_extension.lower()
Callback used by get_deferred_field_names().
dataset/ETHPy150Open NVIDIA/DIGITS/tools/download_data/downloader.py/DataDownloader.__init__--crossover with--dataset/ETHPy150Open django/django/django/db/models/sql/query.py/Query.get_loaded_field_names_cb