a new subprocess.call which raises an error on non-zero rc

[ncw]

BPO	1071764
Files	xcall.patch: patch for subprocess to implement raising call xcall.patch: Adapted patch against trunk

^{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 = None
closed_at = <Date 2005-01-01.09:37:48.000>
created_at = <Date 2004-11-23.14:45:22.000>
labels = ['library']
title = 'a new subprocess.call which raises an error on non-zero rc'
updated_at = <Date 2005-01-01.09:37:48.000>
user = 'https://bugs.python.org/ncw'

bugs.python.org fields:

activity = <Date 2005-01-01.09:37:48.000>
actor = 'astrand'
assignee = 'astrand'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2004-11-23.14:45:22.000>
creator = 'ncw'
dependencies = []
files = ['6373', '6374']
hgrepos = []
issue_num = 1071764
keywords = ['patch']
message_count = 5.0
messages = ['47326', '47327', '47328', '47329', '47330']
nosy_count = 2.0
nosy_names = ['astrand', 'ncw']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1071764'
versions = ['Python 2.5']

[ncw]

The attached patch introduces a 3rd utility function -
xcall() to the
subprocess module. This function acts just like call
but raises
errors if the command had a non-zero return code.

This saves writing

if call(...):
    raise OSError(...)

It is most useful for shell script replacement
programming. Checking
the return codes of commands called is often forgotten
in shell
programming.

When you've moved up to python because shell is too
limiting (usually
about 10 lines of shell in my case ;-) you want to make
sure that all
your commands work so you write robust code.

I consider raising an exception to be much more
pythonic than checking
a return code (ie "Errors should never pass silently"
from Zen of
Python)

Eg

# An easy to miss error

>>> subprocess.call(["mkdir", "a/b"])
mkdir: cannot create directory `a/b': No such file or
directory
1
>>> # user forgot to check non-zero return code

# becomes an impossible to miss exception

>>> subprocess.xcall(["mkdir", "a/b"])
mkdir: cannot create directory `a/b': No such file or
directory
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "subprocess.py", line 462, in xcall
    raise CalledProcessError(rc, "Command %s returned
non zero exit status" % args[0])
subprocess.CalledProcessError: [Errno 1] Command
['mkdir', 'a/b'] returned non zero exit status
>>> 

See attached patch for more! Its been tested under
python 2.3 on
windows and linux.

[astrand]

Logged In: YES
user_id=344921

Since this is a new feature, the patch will go into trunk,
but not the 2.4 maint branch.

[astrand]

Logged In: YES
user_id=344921

My suggested name is "check_call".

[astrand]

Logged In: YES
user_id=344921

If there are no objections, I will commit the "Adapted patch
against trunk".

[astrand]

Logged In: YES
user_id=344921

Patch applied. New revisions:

subprocess.py 1.12
test_subprocess.py 1.17
libsubprocess.tex 1.5