Fix B006 lint errors: using mutable structure in default argument. (#18178)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18178
ghimport-source-id: 667ee76b418f505fa64b863e52a603c508dcd1bf
Stack from [ghstack](https://github.com/ezyang/ghstack):
* #18184 Fix B903 lint: save memory for data classes with slots/namedtuple
* #18181 Fix B902 lint error: invalid first argument.
* **#18178 Fix B006 lint errors: using mutable structure in default argument.**
* #18177 Fix lstrip bug revealed by B005 lint
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Differential Revision: D14530874
fbshipit-source-id: 38f4456a085bfe55f2a96fff53028ebd0d621604
