* Reformat sdk only using the new yapf config.
* Reformat docstrings using docformatter.
* update golden files to resolve diff caused by whitespaces
* fix some tests
* format .py files under sdk/python/tests using yapf
* additional docformatter
* fix some tests
* handle type annotation with Optional
* remove typing._GenericAlias, which is available only after Py 3.7
* fix
* fix py3.6 test
* address review comments