Em Dom, 2008-11-02 às 17:51 -0800, mabshoff escreveu:
>
>
> On Nov 2, 5:32 pm, Ronan Paixão <[EMAIL PROTECTED]> wrote:
> > Em Dom, 2008-11-02 às 16:26 -0800, William Stein escreveu:
> >
> >
> >
> > > On Sun, Nov 2, 2008 at 4:15 PM, Ronan Paixão <[EMAIL PROTECTED]> wrote:
> >
> > > > don't know if this is "the right"(tm) way to do it, but it seems more
> > > > pythonic:
> >
> > > > import os
> > > > [p for p in os.environ['PATH'].split(':') if os.path.exists('%s/%s' %
> > > > (p,'phc'))]
> >
> > > > which should return a list with the paths in which the file 'phc'
> > > > exists, or an empty list if it doesn't
> >
> > > > Ronan Paixão
> >
> > > That is unfortunately not equivalent to the unix which command.
> > > For example, if the file phc appears anywhere in the path it will
> > > get included. The which command instead will tell you whether
> > > or not there is an *executable* called phc that is in the path.
> > > So that's a subtle difference.
> >
> > > -- William
> >
> > Sure, there some subtle difference
> > that can be overcome with some changes:
> >
> > import os
> > try:
> > filename = [p for p in os.environ['PATH'].split(':') if
> > os.path.exists('%s/%s' % (p,'phc'))] + "/phc"
> > s = os.stat(filename)[0]
> > if not s & 0x49: #sees if at least one exec bit is set
>
> It is not sufficient that at least one exec bit is set, it has to be
> the right one depending on ownership. I really don't see any benefit
> over using "which" - aside from the fact that some versions of which
> do not return an error code unequal zero when no binary is found.
>
That's exactly what I meant by "might require more voodoo to see if the
user itself can exec it".
I just sketched the code because doing it in Python might be more
portable, but thinking again, you probably won't get exec attributes in
non-Unix systems anyway (though I'm not sure how os.stat handles that).
However, since porting it to Windows might be a Sage target one day,
doing it the "hard way" (which probably should include more thinking)
may be desirable.
Ronan Paixão
> > #might require more voodoo to see if
> > #the user itself can exec it
> > raise
> > except:
> > raise ValueError, "phc not found"
>
> Cheers,
>
> Michael
> >
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