bug in os.system?

The following code fails (pythonbugtest.exe takes one parameter, a
string):

import os
result = os.system('"pythonbugtest.exe" "test"')
assert(result == 0)

The error message is:

'pythonbugtest.exe" "test' is not recognized as an internal or external
command, operable program or batch file.
Traceback (most recent call last):
File "C:\Nick\!My Programs\Python\bugtest\python1.py", line 8, in ?
assert(result == 0)
AssertionError


If I remove the quote marks around "pythonbugtest.exe" or "test", it
works fine. But sometimes I need those quote marks, if e.g. there are
spaces in filenames.

I think this is a bug?

I'm running Python 2.4.1 on Windows XP Pro.

nicksjacobson@yahoo.com

What happens when you try it without the single quotes?
result = os.system("pythonbugtest.exe" "test")

wrote:
> What happens when you try it without the single quotes?
> result = os.system("pythonbugtest.exe" "test")
>
That would be equivalent to

result = os.system("pythonbugtest.exetest")

which almost certainly won't do anything useful.

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC www.holdenweb.com
PyCon TX 2006 www.python.org/pycon/

wrote:

> The following code fails (pythonbugtest.exe takes one parameter, a
> string):
>
> import os
> result = os.system('"pythonbugtest.exe" "test"')
> assert(result == 0)
>
> The error message is:
>
> 'pythonbugtest.exe" "test' is not recognized as an internal or external
> command, operable program or batch file.
> Traceback (most recent call last):
> File "C:\Nick\!My Programs\Python\bugtest\python1.py", line 8, in ?
> assert(result == 0)
> AssertionError
>
> If I remove the quote marks around "pythonbugtest.exe" or "test", it
> works fine. But sometimes I need those quote marks, if e.g. there are
> spaces in filenames.
>
> I think this is a bug?

yup, but unfortunately, it's a bug at the windows level, not in Python. from what
I can tell, the problem is that cmd.exe cannot parse the command string it's given
by the C-level system() call.

possible workarounds:

1. get rid of the quotes around the command name:

result = os.system('pythonbugtest.exe "test"')

2. add an extra quote (!) before the quoted command name:

result = os.system('""pythonbugtest.exe" "test"')

3. use os.spawn or the subprocess module instead.

</F>

OK, I give up. Why does workaround #2 work?

Also, I didn't realize this before, but when you call os.spawnv, the
argument list you pass starts with the name of the executable you're
calling! When you call a program from cmd.exe, that program name is
the first parameter automatically. But with spawnv, you do that
manually!

Anyway, thanks for your help!

wrote:
> OK, I give up. Why does workaround #2 work?

Well, there was a time when the cmd prompt treated all
spaces as delimiters, so

>cd My Documents

would fail. Nowadays you can do that successfully and even

>cd My Documents\My Pictures

works.

In the old days, if a directory had a space, you had to
enclose it in quotes

>cd "My Documents"

But you didn't actually need to include the trailing quote,
so you could get away with

>cd "My Documents

I'm sure if you looked it up, Microsoft would say

This behaviour is by design.


>
> Also, I didn't realize this before, but when you call os.spawnv, the
> argument list you pass starts with the name of the executable you're
> calling! When you call a program from cmd.exe, that program name is
> the first parameter automatically. But with spawnv, you do that
> manually!
>
> Anyway, thanks for your help!