I was thinking about "yield from" and how many times I wanted to use the feature, but because of backward compatibilities, I couldn't.

It's sad that it may take possibly 5 or 10 years to see this statement being used in real programs... The PEP 380 was proposed while Python3.1 was still alpha or beta and it took two and a
half years to be accepted, but once it was, Python3.2 was already released.

I don't know if this was proposed before, but why can't Python have an "__experimental__"
magic package for this kind of stuff?
The __future__ thing already add features that are sure to be included on a future
release, but why those that may become official have to suffer that much?

What if an experimental feature becomes rejected?

from __experimental__ import foo

DeprecationWarning: "foo" will be removed on Python 4.0

Note that the idea is not for people to use experimental features when they appear,
but to have a fallback for when the feature becomes official!

As side effect, the feature will be more tested and become more mature when released.

João Bernardo