I just installed Python 2.7 on my new project because some critical libraries used by the customer don't care Python 3 exists.

Open source ones?

To some extent yes, and no I am not going to mention which ones.

I just can't think of a major open source python lib that hasn't added support for 3 if the functionality wasn't replaced by a new feature in 3.

Github is a tiny drop on the universe from enteprise computing.

You get 10 years of headaches for everyone who gets close to the language. Even today, the python executable in Ubuntu is called `python3`, not `python`.

To be fair though, it would be less of a problem for C++ than it was for Python, since you wouldn't have to depend on the compiler from the end-user system.