[Tutor] subprocess.call list vs. str argument

[Peter Otten]

Albert-Jan Roskam wrote:

> Hi,
> 
> In the code below, cmd1 and cmd2 are equivalent, as in: " ".join(cmd1) ==
> cmd2. But the first example returns a code 2, whereas the second runs
> successfully. What is the difference? I prefer using a list as it looks a
> little cleaner. Btw, shell=True is needed here.
> 
> 
> # Python 2.7.3 (default, Jan  2 2013, 13:56:14) [GCC 4.7.2] on linux2
> 
> import subprocess
> 
> #1# returns retcode 2 (whatever error that maybe)
> title, author, version = "title", "author", "1.0.0"
> output_dir, input_dir = '/tmp/input', '/tmp/output'
> cmd1 = [r'sphinx-apidoc',
> r'-f -F',
> r'-H', '"%s"' % title,

"title" becomes \"title\", i. e. Python puts in an extra effort to have the 
quotes survive the subsequent parsing process of the shell:

>>> print subprocess.list2cmdline(['"title"'])
\"title\"


> r'-A', '"%s"' % author,
> r'-V', '"%s"' % version,
> r'-o', output_dir, input_dir]
> retcode = subprocess.call(cmd1, shell=True)
> assert not retcode, retcode
> 
> #2# returns retcode 0 (succes)
> cmd2 = (r'sphinx-apidoc '
> r'-f -F '
> r'-H "%(title)s" '
> r'-A "%(author)s" '
> r'-V "%(version)s" '
> r'-o %(output_dir)s %(input_dir)s') % locals()
> 
> retcode = subprocess.call(cmd2, shell=True)
> assert not retcode, retcode
> 
> # no AssertionError
> assert " ".join(cmd1) == cmd2
> 
> 
> 
> Thanks in advance!
> 
> Regards,
> 
> Albert-Jan
> 
> 
> 
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> All right, but apart from the sanitation, the medicine, education, wine,
> public order, irrigation, roads, a
> 
> fresh water system, and public health, what have the Romans ever done for
> us?
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> To unsubscribe or change subscription options:
> https://mail.python.org/mailman/listinfo/tutor