[Python-Dev] (name := expression) doesn't fit the narrative of PEP 20

[Tim Peters]

[Raymond Hettinger <raymond.hettinger at gmail.com>]
> After re-reading all the proposed code samples, I believe that
> adopting the PEP will make the language harder to teach to people
> who are not already software engineers.

Can you elaborate on that?  I've used dozens of languages over the
decades, most of which did have some form of embedded assignment.
Yes, I'm a software engineer, but I've always pitched in on "help
forums" too.  One language feature conspicuous by absence in newbie
confusions was, consistently, assignment expressions.  Read any book
or tutorial for such a language, and you'll find very little space
devoted to them too.

What's to learn?  If they understand "binding a name" _at all_ (which
they must to even begin to write a non-trivial program), the only
twist is that a binding expression returns the value being bound.
Binding expressions certainly wouldn't be the _first_ thing to teach
people.  But by the time it would make sense to teach them, it's hard
for me to grasp how a student could struggle with such a tiny
variation on what they've already learned (all the subtleties are in
what - exactly - "binding"means - which they already faced the first
time they saw "j = 1").


> To my eyes, the examples give ample opportunity for being
> misunderstood and will create a need to puzzle-out the intended semantics.

Some do, many don't.  The same can be said of a great many constructs ;-)

> ...