Summary:
DPER has very strange python ops that play with Workspace - they are somewhat similar to LoadOp/SaveOp, so I guess the semantics is fine.
Thus it makes sense to allow python operators to receive workspace pointer similarly to regular Operators.
I didn't figure out a better way to implement optional argument than just checking the number of args function receives on python side.
Reviewed By: ajtulloch
Differential Revision: D4242943
fbshipit-source-id: d97d4227815b741c8f884cfe254b06d2b56b5a41