Redux of #2. At some point, we should drop Python 2 support. Python 2 is EOL'ed (2020), surveys suggest that Python 2 usage is approaching single digits in the near future (if this has not happened already).

In my opinion, two major features in Python 3 which would greatly benefit PyTorch:

• Native type hint syntax
• Async/await

Possible timelines:

• Stop supporting Python 2 immediately after 1.2 release (this is unlikely to happen)
• Stop supporting Python 2 in PyTorch at the same time Python 2 is EOL'ed (beginning of 2020)
• Continue to support Python 2 for some indefinite period of time after 2020 EOL, until we see that Python 2 usage has dropped sufficiently for us to drop it