Add python string standard lib (#21807)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21807
ghimport-source-id: dcb2c78b8facb90a323ab9212b7703e553354273
Test Plan: Imported from OSS
Differential Revision: D15835509
Pulled By: bwasti
fbshipit-source-id: bc8bc5ae5a4fb4a1581aa94485973ed87af4eaaf
