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

[Steven D'Aprano]

On Thu, Apr 26, 2018 at 10:34:29PM +1200, Greg Ewing wrote:
> Antoine Pitrou wrote:
> >Well, how do languages where assignment is an expression returning the
> >assigned value make their REPLs work?  I'm sure they don't inflict that
> >on their users, so it's certainly a solvable problem.
> 
> I can't think of any such language that has a REPL
> offhand, but here's a possible solution:


Here's the Rhino Javascript REPL:

[steve at ando ~]$ rhino
Rhino 1.7 release 0.7.r2.3.el5_6 2011 05 04
js> x = (a = 99) + 1
100


Here's the standard Ruby REPL:

[steve at ando ~]$ irb
irb(main):001:0> x = (a = 99) + 1
=> 100


So both of these REPLs do print the result of the expression.

R, on the other hand, doesn't print the results of assignment 
expressions:

> x <- (a <- 99) + 1
> c(x, a)
[1] 100  99

Rhino, however, does suppress printing if you prefix the variable with 
"var" or "const".



-- 
Steve