bpo-37972: unittest.mock._Call now passes on __getitem__ to the __getattr__ chaining...

bpo-37972: unittest.mock._Call now passes on __getitem__ to the __getattr__ chaining so that call() can be subscriptable (GH-15565) (GH-15965)

* bpo-37972: unittest.mock._Call now passes on __getitem__ to the __getattr__ chaining so that call() can be subscriptable

* 📜🤖 Added by blurb_it.

* Update 2019-08-28-21-40-12.bpo-37972.kP-n4L.rst

added name of the contributor

* bpo-37972: made all dunder methods chainable for _Call

* bpo-37972: delegate only attributes of tuple instead to __getattr__
(cherry picked from commit 72c359912d36705a94fca8b63d80451905a14ae4)

Co-authored-by: blhsing <github@ydooby.com>