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context managers inline?

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  context managers inline? Neal Becker <ndbecker2@gmail.com> - 2016-03-10 13:33 -0500
    Re: context managers inline? sohcahtoa82@gmail.com - 2016-03-10 10:47 -0800
      Re: context managers inline? Neal Becker <ndbecker2@gmail.com> - 2016-03-10 13:59 -0500
      Re: context managers inline? Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-10 12:19 -0700
      Re: context managers inline? jmp <jeanmichel@sequans.com> - 2016-03-11 11:42 +0100
    Re: context managers inline? Steven D'Aprano <steve@pearwood.info> - 2016-03-11 15:35 +1100

#104538 — context managers inline?

Is there a way to ensure resource cleanup with a construct such as:

x = load (open ('my file', 'rb))

Is there a way to ensure this file gets closed?

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#104540

On Thursday, March 10, 2016 at 10:33:47 AM UTC-8, Neal Becker wrote:
> Is there a way to ensure resource cleanup with a construct such as:
> 
> x = load (open ('my file', 'rb))
> 
> Is there a way to ensure this file gets closed?

with open('my file', 'rb') as f:
    x = load(f)

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#104542

sohcahtoa82@gmail.com wrote:

> On Thursday, March 10, 2016 at 10:33:47 AM UTC-8, Neal Becker wrote:
>> Is there a way to ensure resource cleanup with a construct such as:
>> 
>> x = load (open ('my file', 'rb))
>> 
>> Is there a way to ensure this file gets closed?
> 
> with open('my file', 'rb') as f:
>     x = load(f)

But not in a 1-line, composable manner?

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#104543

On Thu, Mar 10, 2016 at 11:59 AM, Neal Becker <ndbecker2@gmail.com> wrote:
> sohcahtoa82@gmail.com wrote:
>
>> On Thursday, March 10, 2016 at 10:33:47 AM UTC-8, Neal Becker wrote:
>>> Is there a way to ensure resource cleanup with a construct such as:
>>>
>>> x = load (open ('my file', 'rb))
>>>
>>> Is there a way to ensure this file gets closed?
>>
>> with open('my file', 'rb') as f:
>>     x = load(f)
>
> But not in a 1-line, composable manner?

def with_(ctx, func):
    with ctx as value:
        return func(value)

x = with_(open('my file', 'rb'), load)


Seems less readable to me, though.

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#104607

On 03/10/2016 07:59 PM, Neal Becker wrote:
> sohcahtoa82@gmail.com wrote:
>
>> On Thursday, March 10, 2016 at 10:33:47 AM UTC-8, Neal Becker wrote:
>>> Is there a way to ensure resource cleanup with a construct such as:
>>>
>>> x = load (open ('my file', 'rb))
>>>
>>> Is there a way to ensure this file gets closed?
>>
>> with open('my file', 'rb') as f:
>>      x = load(f)
>
> But not in a 1-line, composable manner?
>

You you really want a 1 liner

with open('my file', 'rb') as f: print 'foo'; x = load(f)


jm

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#104580

On Fri, 11 Mar 2016 05:33 am, Neal Becker wrote:

> Is there a way to ensure resource cleanup with a construct such as:
> 
> x = load (open ('my file', 'rb))
> 
> Is there a way to ensure this file gets closed?

Depends on what you mean by "ensure". Have load() call the file's close
method may be good enough.

If you want a better guarantee, you need either a with block:

with open(...) as f:
    ...


or a finally block:

try:
    ...
finally:
    ...


There is no expression-based version of these.



-- 
Steven

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