add double caching for yelp polarity to speed up extracted reading. (#1530)
add double caching for yelp polarity to speed up extracted reading. (#1530)

* add double caching for yelp polarity to speed up extracted reading.

* rename dps for consistency and simplify filepath_fn

* add FileOpener within caching block for more consistency.
pytorch/text,pytorch/text,pytorch/text,pytorch/text