[Python-ideas] if <expression> as <variable>

[Steven D'Aprano]

On Thu, Sep 07, 2017 at 04:36:40PM +0200, Jason H wrote:

> I also often wonder why we are left doing an assignment and test. You have two options:
> 1. assign to a variable then test and use
> 2. repeat the function call

Personally, I don't see what's wrong with the "assign then test" idiom.

x = something()
if x:
    do_stuff()

 
> I would offer that 'with' [sh|c]ould be used:
> with test() as x:
>    handle_truthy(x)
> else:
>    handle_falsey() # do we provide x here too? Because None vs False?


This would cause confusing errors and mysterious behaviour, depending on 
whether the test() object was a context manager or not. Which should 
take priority? If you see:

with spam() as x:
   do_stuff

is that a context manager with block (like "with open(...) as f") or 
your boolean if test in disguise?

Having "with" sometimes be a disguised "if" and sometimes a regular 
"with" will make it really, really hard to reason about code.


-- 
Steve