subprocess (Replacing popen) - add a warning / hint

[HWJ]

BPO	2947
Nosy	@birkenfeld, @bitdancer
Files	issue2947-doc.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/bitdancer'
closed_at = <Date 2009-06-09.00:47:38.997>
created_at = <Date 2008-05-22.15:17:54.047>
labels = ['easy', 'type-feature', 'docs']
title = 'subprocess (Replacing popen) - add a warning / hint'
updated_at = <Date 2009-06-09.00:47:38.996>
user = 'https://bugs.python.org/HWJ'

bugs.python.org fields:

activity = <Date 2009-06-09.00:47:38.996>
actor = 'r.david.murray'
assignee = 'r.david.murray'
closed = True
closed_date = <Date 2009-06-09.00:47:38.997>
closer = 'r.david.murray'
components = ['Documentation']
creation = <Date 2008-05-22.15:17:54.047>
creator = 'HWJ'
dependencies = []
files = ['14218']
hgrepos = []
issue_num = 2947
keywords = ['patch', 'easy']
message_count = 4.0
messages = ['67195', '89047', '89068', '89131']
nosy_count = 3.0
nosy_names = ['georg.brandl', 'HWJ', 'r.david.murray']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue2947'
versions = ['Python 2.6', 'Python 3.0', 'Python 3.1', 'Python 2.7']

[HWJ]

Background:
I (as many others, too) have used the following code in the past

ARC='MyDumpFile'
tar_inp= os.popen('/bin/tar cjf '+ARC+' -T -','w')
....
tar_exit_code= tar_inp.close()
if  tar_exit_code != None and tar_exit_code % 256 :
  print "some error messages"

When replacing this - as suggested - by

TAR= Popen(('/bin/tar','cjf',ARC,'-T','-'),stdin=PIPE)
tar_inp= TAR.stdin
....
tar_inp.close() always returns None which was an indication
of NO ERROR when used together with popen.

So this has proabaly to be replaced by

tar_inp.close()
tar_exit_code= TAR.wait()

if  tar_exit_code != 0 :
  print "some error messages"

I suggest a warning / hint to change checking for errors
when upgrading to subprocess.Popen

[bitdancer]

Patch attached that adds an example that shows how to translate return
code handling, loosely based on Helmut's example. I also turned the
function references in the section titles into links because I think
that would be very useful to someone wanting to do a translation
(provides easy access to the docs for the old functions). The font size
looks a bit weird in the generated docs, though, so perhaps that is why
this wasn't done originally. If putting references in section titles is
a no-no let me know and I'll remove them from the patch.

Also included in the patch is a fix for the cross reference link from
the os.spawn section to the 'replacing functions' section of the
subprocess docs.

[birkenfeld]

Patch looks good, except for strange code indentation in the replaced
example.

[bitdancer]

Applied (with spacing fix) in r73313.