[Python-ideas] Statements vs Expressions... why?

[Cliff Wells]

On Thu, 2008-09-11 at 14:56 -0400, Mike Meyer wrote:
> Here's where we disagree. I love functional programming, having
> written 10s of thousands of lines of LISP in the past. The lack of the
> ability to pass around functions in Ruby is why I haven't ever written
> any. 

You can:

def a(x,y)
    x + y
end

def x(b)
    send(b,3,4)
end

puts x(:a)  # 7

The semantics are a bit different, but the result is the same (caveat:
I'm no Ruby expert by any stretch of the imagination).

Anyway, not important =)

> And I consider the results of trying to cram python statements
> into expressions as almost universally ugly. I'm willing to consider
> you might have a solution, but you refuse to *show* it to me.

I'm not sure what else you'd like to see.  I've provided an example with
a for-loop as generator and if-expressions.  I've no intention of
writing a full PEP covering all use-cases at this point.

> > Overall, if you are familiar with functional programming, it doesn't
> > take a lot to imagine more examples.  If you aren't, then it probably
> > won't make much sense or seem too appealing in any case.
> 
> You're right - it's easy to image in more examples. Really, really
> ugly ones, like:
> 
>      a = (
>        	  if x < 23:
> 	     18
> 	  else:
> 	     24
> 	 ) + (
> 	      if y < 23:
> 	          29
> 	      else:
> 	          81
>              )
> 
> The thought of running into something like the above in production
> code is enough to make me bounce pretty much any proposal that would
> allow it. Compared to that,
> 
>    a = (18 if x < 23 else 24) + (29 if y < 23 else 81)

a = ( if x < 23: 18 else: 24 ) + ( if y < 23: 29 else: 81 )

Granted, today this is not valid Python, but supporting it doesn't seem
to break existing Python code either.  This is precisely how Logix does
it (from the page I linked you to earlier):

x = if 2+2==4: "I thought so" else: "hmmm..."

In any case, your above code seems intentionally formatted to be
unreadable, something that could be achieved under any circumstances.
For example, here's your code reformatted in a fashion similar to your
first example:

a = (
     18 
     if x < 23 
     else 24
    ) + (
         29 
         if y < 23 
         else 81
        )

Just as unreadable (although really I don't find it terrible to
comprehend... certainly no worse than a complicated listcomp).  
At the end of the day, no programming language is going to be able to
enforce sane coding style (even Python's whitespace can be circumvented
to a large degree).

What we do gain with the idea I've forwarded is a single, more flexible
if-expression in place of an if-statement and an if-operator with
inverted syntax.

Regards,
Cliff