Need a cross-platform way to execute binary

[techtonik]

On Feb 10, 12:03 pm, "Gabriel Genellina" <gagsl... at yahoo.com.ar>
wrote:

> > Does anybody know simple cross-platform method of probing if
> > executable binary is available and launching it.
>
> > Problem no.1: test if executable file is available
> > I'll take windows platform as the most relevant in this case.
> > os.access() doesn't handle env PATHEXT and can't detect if a given
> > path would be executable or not. Here "executable" means file that
> > could be be launched by system() (if there are any other ways - I'd be
> > happy to know them)
>
> > Suppose I have "ufo2exe" executable two directories up.
> >>>> os.access("../../ufo2map.exe", os.X_OK)
> > True
>
> > However...
> >>>> os.access("../../ufo2map", os.X_OK)
> > False
>
> That's right - such file does not exist. On Windows, in general, X_OK is
> the same as F_OK: for any existing file, whatever name or extension,
> returns True. Permissions are managed thru ACL and this simple function
> does NOT consider them.

It shouldn't matter if the file exists or not. Quoting http://
docs.python.org/lib/os-file-dir.html:
"
X_OK
     Value to include in the mode parameter of access() to determine
if path can be executed.
"

See - there is no "file" notation as only "path" is tested and "path"
is pretty executable. I think this should be clarified in os.access()
documentation to make the whole business less confusing if not
implemented in interpreter itself. After all the purpose of cross-
platform language is to free developer from writing platform-specific
code.

>
> > But...
> >>>> os.system("..\..\ufo2map")
> > ---- ufo2map 1.0 ----
> > 0
>
> (Beware of single \ on normal strings!)
> Use win32api.FindExecutable; should return the full path to ufo2map.exe.
> "foo.txt" would return notepad.exe (or whatever you have associated to
> text files). That is exactly what would be launched by os.system("foo.txt")

Why isn't it possible to integrate the functionality in os.access() -
IIUC Python interpreter still uses Windows API itself on this
platform.

> > Problem no.2: launch executable file
> > The same windows platform again. All python commands are using forward
> > slashes for paths, but system doesn't handle this situation (it could
> > at least try to convert immediate forward slashes to backwards)
>
> Use os.path.normpath on the filename. (If you got it from FindExecutable
> above, that would not be needed)
>
> > os.access() thinks this file is executable, but os.system() fails ...
> >>>> os.access("../../ufo2map.exe", os.X_OK)
> > True
> >>>> os.system("../../ufo2map.exe")
> > '..' is not recognized as an internal or external command,
> > operable program or batch file.
> > 1
>
> > the contrary - access() fails to tell this path can be launched, but
> > file Is executable,  ...
> >>>> os.access("..\..\ufo2map", os.X_OK)
> > False
>
> Same as above - such file does not exist.

Same as above - access() tests path, not file, so the argument is not
valid.

> >>>> os.system("..\..\ufo2map")
> > ---- ufo2map 1.0 ----
> > 0
> > Is there any workaround in Python or I have to stick with platforms-
> > specific quirks?
> > I'm using Python 2.4.2
>
> I think you will have to treat each platform differently. Just for
> starting, the concept of "executable" is not the same across platforms.
> But you could make some generic functions (with different implementations
> on different platforms).

I would prefer to know as little about underlying platforms as
possible.
It would only be a big plus for Python.

--
--t.