Codecov Report

Merging #18264 into master will increase coverage by 1.07%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master   #18264       +/-   ##
===========================================
+ Coverage   82.12%   83.19%    +1.07%     
===========================================
  Files        1955     1570      -385     
  Lines      588723   414212   -174511     
  Branches    44383    44401       +18     
===========================================
- Hits       483465   344607   -138858     
+ Misses      95630    59966    -35664     
- Partials     9628     9639       +11     

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According to https://docs.python.org/3/reference/expressions.html#evaluation-order expressions within a list are evaluated left to right. So, [*None, print("XXX")] should not print "XXX" as *None should be evaluated first and raise a TypeError.
Also compare with [+None, print("XXX")], [None[:], print("XXX")] and [None(), print("XXX")]

In the expression [a, b] a should be fully evaluated before b.

The same rationale applies to ** unpacking.

I don't think I agree.

According to https://docs.python.org/3/reference/expressions.html#evaluation-order expressions within a list are evaluated left to right.

In the expression [a, b] a should be fully evaluated before b.

Absolutely, 100%. And in [*a, *b], the same holds. *a is not an expression, though!

"Unary *" isn't an operator; it doesn't appear on the operator precedence table at the link you provided, and you can't evaluate *x. Like the brackets and the comma, it's part of the syntax of the outer display expression, not the inner one. It specifies how the list should be built, so it should be evaluated last, as part of the list construction (as it always has been).

I think one of the examples in the link you provided is the most clarifying here:

In the following lines, expressions will be evaluated in the arithmetic order of their suffixes:

...
expr1(expr2, expr3, *expr4, **expr5)
...

Note that the stars are not part of expressions 1-5, but are a part of the top-level call expression that operates on them all.