[Python-Dev] Is PEP 572 really the most effective way to solve the problems it's targeting?

[Steven D'Aprano]

On Wed, Apr 25, 2018 at 09:36:31PM -0500, Ryan Gonzalez wrote:
> <opinion>
> 
> I have to say I'm not overly thrilled with PEP 572...it's almost odd, 
> because if you asked me back when I first joined this list when I was 13, I 
> would've no doubt said *YES*.

I have the opposite experience: I've warmed to it the more I have read 
it. Before Chris had even written this PEP, there was a Python-Ideas 
thread asking for dedicated syntax in comprehensions alone that would 
have been equivalent to a binding-expression. I was rather negative 
about the whole thing (but no where near as negative as I've been in 
the past when this has come up before), until Chris pointed out that 
such binding-expressions have value outside of comprehensions.


[...]
> Now, what's the common theme here? **Declarations should be separate from 
> expressions.**

Declarations and assignments are not the same thing.


> We've got languages that range from baggage-filled to 
> functional to a bit of all of the above, and none of them have added 
> assignment *inside* an expression.

And your claim about assignment inside expressions is only true if you 
ignore the languages where assignment is an expression with a return 
value. You know, strange and exotic languages with hardly any users or 
influence, like C, C++, C#, Java, Javascript, Ruby, Perl, PHP, Lisp ... 


-- 
Steve