* Fix hola's multiple choice question.

* introduce utils.cache with tests

* import operator

* add trailing newline

* trailing newlines

* introduce FileCache to speed up lint checks

* remove old open

* fixes

* fix superfluous-parens

* nit fixes

* reorganization

* revert utils.cache

* remove unused import

* s/readlines/read_lines/

* use readlines on builtin file obj

* merge get_data with get_lock

* improvements to _FileCache

* make FileCache public

* avoid locking as much as possible

* access FileCache directly

* simpler naming

* remove unused import

* improve str usages

* get lock in separate method