Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Peter Otten <__peter__@web.de>
Newsgroups: comp.lang.python
Subject: Re: Request More Help With XBM Image
Date: Tue, 01 Mar 2016 19:26:55 +0100
Organization: None
Lines: 72
Message-ID: <mailman.77.1456856833.20602.python-list@python.org>
References: <8rKdnb6SKYLRIEnLnZ2dnUU7-f3NnZ2d@giganews.com> <mailman.60.1456822634.20602.python-list@python.org> <34GdnUOxhd5vS0jLnZ2dnUU7-Y3OydjZ@giganews.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7Bit
User-Agent: KNode/4.13.3
Precedence: list
Xref: csiph.com comp.lang.python:103812

Wildman via Python-list wrote:

> On Tue, 01 Mar 2016 09:56:56 +0100, Peter Otten wrote:

>> Wildman via Python-list wrote:

>>> convert = "convert " + fileName + " -resize 48x48! -threshold 55% xbm:-"
>>> p = subprocess.Popen([convert], stdout=subprocess.PIPE, shell=True)
>>> xbmFile, err = p.communicate()

>> Why would you need a shell?

Just in case the example in my previous post has not made it clear: that was 
a rhetorical question. You do not need the shell, and in fact shouldn't use 
it.

> I guess it is a Linux thing.  If I don't use it, I get
> the below error.  A shell window does not actually open.
> I presume it runs in the background while executing the
> subprocess command.

> Exception in Tkinter callback
> Traceback (most recent call last):
> File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1535, in __call__
> return self.func(*args)
> File "./test.py", line 59, in open_image
> p = subprocess.Popen(command, stdout=subprocess.PIPE)
> File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
> errread, errwrite)
> File "/usr/lib/python2.7/subprocess.py", line 1335, in _execute_child
> raise child_exception
> OSError: [Errno 2] No such file or directory
 
An exception is raised because you pass the command as a single argument 
like in

[Python 2.7]
>>> subprocess.Popen("ls /usr/share/dict/words")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1327, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

This looks for an executable called "ls /usr/share/dict/words" (the whole 
shebang!) where you actually want to run "ls" with the argument 
"/usr/share/dict/words". 

Once you split the parts

>>> subprocess.Popen(["ls", "/usr/share/dict/words"])
<subprocess.Popen object at 0x7fa6286d6250>
>>> /usr/share/dict/words

everything works as expected.

The error message in Python 3.4 would have given you a clue, by the way:

[Python 3.4]
>>> subprocess.Popen("ls /usr/share/dict/words")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/subprocess.py", line 859, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1457, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'ls 
/usr/share/dict/words'