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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.
__future__ import for assignment expressions?
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Assignment expression are written with a new notation (:=) . This operator is often called the walrus operator as it resembles the eyes and tusks of a walrus on its side. The assignment expression allows you to assign True to walrus , and immediately print the value.
The error is a simple typo: x = 0, which assigns 0 to the variable x, was written while the comparison x == 0 is certainly what was intended.
We can also use assignment expressions in list comprehensions. List comprehensions allow you to build lists succinctly by iterating over a sequence and potentially adding elements to the list that satisfy some condition.
There is new syntax := that assigns values to variables as part of a larger expression.
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:
- 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.
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