Can assignment expressions be enabled in Python 3.7 using __future__?

Question

Python 3.8 introduces assignment expressions, described in PEP 572. Is there a way to test this new feature in Python 3.7.x?

In the past, new language features have been backported to earlier Python versions using __future__ imports.

• Is there a __future__ import for assignment expressions?
• If yes, what is the feature name?
• If no, are there plans to add it? (3.7 is going to be around for a while)

Answer 1

There is no __future__ import for assignment expressions in Python 3.7 – and adding one in a micro (or "bugfix") release is prohibited by PEP 6:

Prohibitions

Bug fix releases are required to adhere to the following restrictions:

1. There must be zero syntax changes. All .pyc and .pyo files must work (no regeneration needed) with all bugfix releases forked off from a major release.

Applicability of Prohibitions

The above prohibitions and not-quite-prohibitions apply both for a final release to a bugfix release (for instance, 2.4 to 2.4.1) and for one bugfix release to the next in a series (for instance 2.4.1 to 2.4.2).

Since assignment expressions constitute a change to the syntax of Python, there's no way they can be added to a future 3.7.x release of Python without breaking this prohibition.