Peerdependency Dataclasses does compromise Python 3.7 and Python 3.8 support (AttributeError: module 'typing' has no attribute '_ClassVar')

[vleandersson]

Overview
There is a known issue, that occurs with many of the packages using Dataclasses where installing Dataclasses actually disrupts the native dataclasses shipped with >Python 3.7.

Example:
When using Pandas v. 1.2.3 together with darwin-py v. 0.5.15 you will encounter the error AttributeError: module 'typing' has no attribute '_ClassVar' due to the usage of @dataclasses.dataclass in pandas/io/common.

Suggested solution

• Deploy a breaking change and lose official support for Python 3.6.
• Add instructions of installing dataclassess 0.6 manually if running on Python 3.6 or below

Workaround
Install package without deps (pip3 install --no-deps) and then manually install all missing dependencies for darwin-py

Downside: A lot of work

How to replicate
I've done this in Docker, as this allows me to run in a clean environment.

1. Spin up a Buster docker image with Python 3.8
2. Install darwin-py==0.5.15
3. Install pandas==1.2.3
4. Import pandas (as pd)
5. Run the docker container

[andreaazzini]

Hi @vleandersson,

We've had an internal discussion recently, and we have decided we are going to drop support for Python 3.6 at the end of the year. That coincides with the final release of Python 3.6. https://www.python.org/dev/peps/pep-0494/#id15