[Python-ideas] Automatic context managers

[Random832]

On 04/26/2013 03:45 PM, Bruce Leban wrote:
>
> On Fri, Apr 26, 2013 at 12:30 PM, Andrew Svetlov 
> <andrew.svetlov at gmail.com <mailto:andrew.svetlov at gmail.com>> wrote:
>
>     On Fri, Apr 26, 2013 at 9:54 PM,  <random832 at fastmail.us
>     <mailto:random832 at fastmail.us>> wrote:
>     > What about a with expression?
>     >
>     > boolean = x.use() with x as open(resource)
>
>     interesting idea. I see nothing bad with proposed construction.
>     Any objections? I've miss something?
>
>
> The most obvious thing as that 'as' is backwards from the with 
> statement. Also this requires you to come up with a name which you 
> have to repeat while
>
>     with(open(resource)).use()
>
>
> doesn't. On the other hand, it allows you to do:
>
>     result = [x.foo(), x.bar()] with open(resource) as x
>
> which opens the way to freewheeling inline assignment:
>
>     @contextmanager
>     def assign(x):
>         yield x
>
>     result = (-b + sqrt(b*b - 4 * a * c)) / (2 * a) with assign(3) as
>     a with assign(4) as b with assign(5) as c
>
>
> I don't think that's a good thing.

If someone wanted to do that, lambda's already here.

(lambda a, b, c: (-b + sqrt(b*b - 4 * a * c)) / (2 * a))(3,4,5)

The original syntax I was going to suggest would have been something 
more along the lines of (with open(resource) as x: x.use()), but figured 
the syntax I ended up posting would be more pythonic (by analogy to list 
comprehensions or if-else)

The purpose of this would be to call cleanup code. Anything can be misused.
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