Go get it here: https://www.python.org/downloads/release/python-390a1/
This is an early developer preview of Python 3.9
Python 3.9 is still in development. This releasee, 3.9.0a1 is the first of six planned alpha releases. Alpha releases are intended to make it easier to test the current state of new features and bug fixes and to test the release process. During the alpha phase, features may be added up until the start of the beta phase (2020-05-18) and, if necessary, may be modified or deleted up until the release candidate phase (2020-08-10). Please keep in mind that this is a preview release and its use is not recommended for production environments.
Many new features for Python 3.9 are still being planned and written. Among the new major new features and changes so far:
The next pre-release of Python 3.9 will be 3.9.0a2, currently scheduled for 2019-12-16.