The issue tracker is used to discuss PEP-level type system issues. However, typing-sig is more appropriate these days.
A copy of the typing module for older Python versions (2.7 and 3.4) is maintained here. Note that the canonical source lives upstream in the CPython repo.
The typing_extensions module lives here.

Workflow

The typing.py module and its unittests are edited in the src subdirectory of this repo. The python2 subdirectory contains the Python 2 backport.

Workflow for PyPI releases

Run tests under all supported versions. As of May 2019 this includes 2.7, 3.4, 3.5, 3.6, 3.7.
On macOS, you can use pyenv <https://github.com/pyenv/pyenv>_ to manage multiple Python installations. Long story short:
- xcode-select --install
- brew install pyenv
- echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
- Open a new shell
- pyenv install 3.5.3
- pyenv install 3.4.6
- (assuming you already have 2.7.13 and 3.6.1 from Homebrew)
- pyenv global system 3.5.3 3.4.6
You can use tox to automate running tests.
Update the version number in setup.py.
Build the source and wheel distributions:
- pip3 install -U setuptools wheel
- pip2 install -U setuptools wheel
- rm -rf dist/ build/
- python3 setup.py sdist bdist_wheel
- rm -rf build/ (Works around a Wheel bug <https://bitbucket.org/pypa/wheel/issues/147/bdist_wheel-should-start-by-cleaning-up>_)
- python2 setup.py bdist_wheel
Install the built distributions locally and test (if you were using tox, you already tested the source distribution).
Make sure twine is up to date, then run twine upload dist/*.