Re: [Python-ideas] Add output() helper function to subprocess module

[Calvin Spealman]

This is probably the most common first use case someone has when trying to
use subprocess for the first time and I think it has always been a bit of a
wart that, given all the helpers and wrappers the subprocess module already
has, it lacks one for that very obvious and common need.

Yes, run() covers everything, but so does subprocess.Popen() itself.
Helpers still help.

On Thu, Apr 4, 2019 at 1:15 PM Guido van Rossum  wrote:

> Let’s please leave this alone. As Serhiy says run() covers everything.
>
> On Thu, Apr 4, 2019 at 3:03 AM Oleg Broytman  wrote:
>
>> On Thu, Apr 04, 2019 at 07:44:29PM +1100, Chris Angelico <
>> ros...@gmail.com> wrote:
>> > On Thu, Apr 4, 2019 at 7:12 PM Nathaniel Smith  wrote:
>> > >
>> > > On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing <
>> greg.ew...@canterbury.ac.nz> wrote:
>> > > >
>> > > > The check_output() function of the subprocess module raises an
>> > > > exception if the process returns a non-zero exit status. This is
>> > > > inconvenient for commands such as grep that use the return
>> > > > status to indicate something other than success or failure.
>> > > >
>> > > > The check_call() function has a companion call(), but here is
>> > > > currently no non-checking companion for check_call(). How
>> > > > about adding one with a signature such as
>> > > >
>> > > > output(args) --> (status, output)
>> > >
>> > > Isn't this already available as: run(args, stdout=PIPE)? Is the object
>> > > to the extra typing, or...?
>> > >
>> >
>> > Or discoverability. If you want to run a subprocess and catch its
>> > output, you'll naturally reach for check_output, and it feels clunkier
>> > to have to use run() instead.
>> >
>> > +1 on adding a nice simple function, although I'm not 100% sold on the
>> > name "output".
>>
>>get_output ?
>>
>> > ChrisA
>>
>> Oleg.
>> --
>> Oleg Broytmanhttps://phdru.name/
>> p...@phdru.name
>>Programmers don't die, they just GOSUB without RETURN.
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>>
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Re: [Python-ideas] Add output() helper function to subprocess module

[Guido van Rossum]

Let’s please leave this alone. As Serhiy says run() covers everything.

On Thu, Apr 4, 2019 at 3:03 AM Oleg Broytman  wrote:

> On Thu, Apr 04, 2019 at 07:44:29PM +1100, Chris Angelico 
> wrote:
> > On Thu, Apr 4, 2019 at 7:12 PM Nathaniel Smith  wrote:
> > >
> > > On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing <
> greg.ew...@canterbury.ac.nz> wrote:
> > > >
> > > > The check_output() function of the subprocess module raises an
> > > > exception if the process returns a non-zero exit status. This is
> > > > inconvenient for commands such as grep that use the return
> > > > status to indicate something other than success or failure.
> > > >
> > > > The check_call() function has a companion call(), but here is
> > > > currently no non-checking companion for check_call(). How
> > > > about adding one with a signature such as
> > > >
> > > > output(args) --> (status, output)
> > >
> > > Isn't this already available as: run(args, stdout=PIPE)? Is the object
> > > to the extra typing, or...?
> > >
> >
> > Or discoverability. If you want to run a subprocess and catch its
> > output, you'll naturally reach for check_output, and it feels clunkier
> > to have to use run() instead.
> >
> > +1 on adding a nice simple function, although I'm not 100% sold on the
> > name "output".
>
>get_output ?
>
> > ChrisA
>
> Oleg.
> --
> Oleg Broytmanhttps://phdru.name/p...@phdru.name
>Programmers don't die, they just GOSUB without RETURN.
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Re: [Python-ideas] Add output() helper function to subprocess module

[Oleg Broytman]

On Thu, Apr 04, 2019 at 07:44:29PM +1100, Chris Angelico  
wrote:
> On Thu, Apr 4, 2019 at 7:12 PM Nathaniel Smith  wrote:
> >
> > On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing  
> > wrote:
> > >
> > > The check_output() function of the subprocess module raises an
> > > exception if the process returns a non-zero exit status. This is
> > > inconvenient for commands such as grep that use the return
> > > status to indicate something other than success or failure.
> > >
> > > The check_call() function has a companion call(), but here is
> > > currently no non-checking companion for check_call(). How
> > > about adding one with a signature such as
> > >
> > > output(args) --> (status, output)
> >
> > Isn't this already available as: run(args, stdout=PIPE)? Is the object
> > to the extra typing, or...?
> >
> 
> Or discoverability. If you want to run a subprocess and catch its
> output, you'll naturally reach for check_output, and it feels clunkier
> to have to use run() instead.
> 
> +1 on adding a nice simple function, although I'm not 100% sold on the
> name "output".

   get_output ?

> ChrisA

Oleg.
-- 
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   Programmers don't die, they just GOSUB without RETURN.
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Re: [Python-ideas] Add output() helper function to subprocess module

[Serhiy Storchaka]

04.04.19 11:59, Greg Ewing пише:

Nathaniel Smith wrote:
On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing 
 wrote:

output(args) --> (status, output)


Isn't this already available as: run(args, stdout=PIPE)?


Yes, but you need to do more than that to get the output
as a string. This is the relevant part of the implementation
of check_output():

     process = Popen(stdout=PIPE, *popenargs, **kwargs)
     output, unused_err = process.communicate()
     retcode = process.poll()



check_output() is currently implemented (besides arguments checks and 
legacy support) as just


run(..., stdout=PIPE, check=True).stdout

For getting unchecked output you need just to omit check=True.

run(..., stdout=PIPE).stdout

I think that after adding run() there is no need in output().

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Re: [Python-ideas] Add output() helper function to subprocess module

[Nathaniel Smith]

On Thu, Apr 4, 2019 at 1:59 AM Greg Ewing  wrote:
>
> Nathaniel Smith wrote:
> > On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing  
> > wrote:
> >>output(args) --> (status, output)
> >
> > Isn't this already available as: run(args, stdout=PIPE)?
>
> Yes, but you need to do more than that to get the output
> as a string. This is the relevant part of the implementation
> of check_output():
>
>  process = Popen(stdout=PIPE, *popenargs, **kwargs)
>  output, unused_err = process.communicate()
>  retcode = process.poll()

>>> from subprocess import run, pipe
>>> p = run(["grep", "njs", "/etc/passwd"], stdout=PIPE)
>>> p.returncode
0
>>> p.stdout
b'njs:x:1000:1000:Nathaniel J. Smith,,,:/home/njs:/usr/bin/zsh\n'

I do think it's a bit weird that you write 'stdout=PIPE' to mean
'please capture stdout' – it's leaking an internal implementation
detail across an abstraction boundary. But it's documented, and run()
allows any combination of check=True/False, capturing stdout or not,
and capturing stderr or not, without having to invent 8 different
functions.

-n

-- 
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Re: [Python-ideas] Add output() helper function to subprocess module

[Chris Angelico]

On Thu, Apr 4, 2019 at 8:02 PM Greg Ewing  wrote:
>
> Chris Angelico wrote:
> > +1 on adding a nice simple function, although I'm not 100% sold on the
> > name "output".
>
> The idea is that output/check_output would go together like
> call/check_call.
>

Yeah, so I think that on balance it's probably the best choice, but as
its own thing, it's a bit odd.

subprocess.output("...")

I'm, let's say, +1 on the idea in general, and +0.9 on calling it "output".

ChrisA
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Re: [Python-ideas] Add output() helper function to subprocess module

[Greg Ewing]

Chris Angelico wrote:

+1 on adding a nice simple function, although I'm not 100% sold on the
name "output".


The idea is that output/check_output would go together like
call/check_call.

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Re: [Python-ideas] Add output() helper function to subprocess module

[Greg Ewing]

Nathaniel Smith wrote:

On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing  wrote:

output(args) --> (status, output)


Isn't this already available as: run(args, stdout=PIPE)?


Yes, but you need to do more than that to get the output
as a string. This is the relevant part of the implementation
of check_output():

process = Popen(stdout=PIPE, *popenargs, **kwargs)
output, unused_err = process.communicate()
retcode = process.poll()

--
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Re: [Python-ideas] Add output() helper function to subprocess module

[Chris Angelico]

On Thu, Apr 4, 2019 at 7:12 PM Nathaniel Smith  wrote:
>
> On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing  
> wrote:
> >
> > The check_output() function of the subprocess module raises an
> > exception if the process returns a non-zero exit status. This is
> > inconvenient for commands such as grep that use the return
> > status to indicate something other than success or failure.
> >
> > The check_call() function has a companion call(), but here is
> > currently no non-checking companion for check_call(). How
> > about adding one with a signature such as
> >
> > output(args) --> (status, output)
>
> Isn't this already available as: run(args, stdout=PIPE)? Is the object
> to the extra typing, or...?
>

Or discoverability. If you want to run a subprocess and catch its
output, you'll naturally reach for check_output, and it feels clunkier
to have to use run() instead.

+1 on adding a nice simple function, although I'm not 100% sold on the
name "output".

ChrisA
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Re: [Python-ideas] Add output() helper function to subprocess module

[Nathaniel Smith]

On Thu, Apr 4, 2019 at 12:48 AM Greg Ewing  wrote:
>
> The check_output() function of the subprocess module raises an
> exception if the process returns a non-zero exit status. This is
> inconvenient for commands such as grep that use the return
> status to indicate something other than success or failure.
>
> The check_call() function has a companion call(), but here is
> currently no non-checking companion for check_call(). How
> about adding one with a signature such as
>
> output(args) --> (status, output)

Isn't this already available as: run(args, stdout=PIPE)? Is the object
to the extra typing, or...?

-n

-- 
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[Python-ideas] Add output() helper function to subprocess module

[Greg Ewing]

The check_output() function of the subprocess module raises an
exception if the process returns a non-zero exit status. This is
inconvenient for commands such as grep that use the return
status to indicate something other than success or failure.

The check_call() function has a companion call(), but here is
currently no non-checking companion for check_call(). How
about adding one with a signature such as

output(args) --> (status, output)

--
Greg
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