[CentralOH] Popen file descriptor difference between Python 2.6 and 2.7+ on Linux

[Thomas Winningham]

oh and the shell=False and stderr = PIPE are not needed that was me just
trying to fudge things somehow and left those in there in that code...
really the pass_fds flag is the thing

On Sat, Feb 17, 2018 at 12:38 AM, Thomas Winningham <winningham at gmail.com>
wrote:

> I was replying on Twitter, but I suspect the behavior slowly became
> undefined somewhere between 2.7 and 3 ... but after 3.2 i can do this and
> it works:
> ------------------------
> from subprocess import Popen, PIPE
>
> data = Popen(
>     ["cat"],
>     stdin=open('/tmp/test', 'rb'),
>     stdout=PIPE,
>     stderr=PIPE,
>     universal_newlines=True,
>     shell=False).stdout
>
> fd_name = '/dev/fd/%d' % data.fileno()
>
> fddata = Popen(
>     ["cat",fd_name],
>     stdout=PIPE,
>     universal_newlines=True,
>     pass_fds=(data.fileno(),)).stdout
>
> print(fddata.read())
> ------------------------
> the "pass_fds" option was added in 3.2 per the subprocess documentation
>
>
> On Fri, Feb 16, 2018 at 11:32 PM, Neil Ludban <nludban at columbus.rr.com>
> wrote:
>
>> On Fri, 16 Feb 2018 22:34:35 -0500
>> Eric Floehr <eric at intellovations.com> wrote:
>> > I have a really odd problem. I have some code that requires a Linux file
>> > descriptor (/dev/fd/N) where N is some number. The following example
>> code
>> > demonstrates effectively what is being done.
>> >
>> > In order to run the code create a file called "/tmp/test" with some
>> text in
>> > it.
>> >
>> > The code works in Python 2.6, but in Python 2.7 or later, I get:
>> >
>> > cat: /dev/fd/4: No such file or directory
>>
>> Smells like a back-porting of adding the O_CLOEXEC flag...
>>
>>      Unless O_CLOEXEC flag was specified, the new descriptor is set to
>> remain
>>      open across execve(2) system calls; see close(2), fcntl(2) and
>> O_CLOEXEC
>>      description.
>>
>> https://www.python.org/dev/peps/pep-0446/
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>>
>
>
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