[Python-ideas] if expensive_computation() as x:

[Steven D'Aprano]

On Fri, Feb 14, 2014 at 05:10:53PM -0500, random832 at fastmail.us wrote:
> On Fri, Feb 14, 2014, at 16:20, Steven D'Aprano wrote:
> > -1 on this. Python is not C and should not emulate it's mistakes, no 
> > matter how tempting they seem :-)
> 
> = as assignment is one of C's mistakes. I propose abandoning it in
> Python 4000.
> 
> Absent that, assignments as expressions is no longer obviously a
> mistake.

I think it is. Mathematicians have been performing algorithmic 
manipulations rather similar to programming for thousands of years, and 
I do not believe that they have anything like assignment as expressions. 
(Or if they do, they're in advanced fields which I have not come 
across.) Instead, they either pre- or post-define the variables they 
need.

# pre-define
y = something complicated related to x
z = function(y + 1/y)

# post-define
z = function(y + 1/y)
where y = something complicated related to x

They don't "in-define":

z = function(something complicated related to x as y + 1/y)


Mathematicians are notorious for inventing user-hostile but terse 
syntax. If they don't do definitions-as-expressions, there is likely to 
be a *really* good reason for it.

C using = for assignment-as-expression just compounds the problem, it 
doesn't create the fundamental problem that sticking assignments in the 
middle of an expression makes the expression hard for human beings to 
parse.



-- 
Steven