Home Original page

Using switches with exec?

Premshree Pillai premshree_python at yahoo.co.in
Mon Jan 12 15:00:25 EST 2004 
 --- Francis Avila <francisgavila at yahoo.com> wrote: >
Premshree Pillai wrote in message ...
> > --- "Diez B. Roggisch" <nospam-deets at web.de>
> wrote: >
> >> I need to run a Python program dynamically within
> >> > another program. I am using exec for the
> purpose.
> >> Is
> >> > there a way to pass parameter switches to exec?
> >>
> >> You can pass a globals-dictionary to exec, which
> can
> >> hold the switches
> >> values.
> >>
> >> Diez
> >> --
> >>
> http://mail.python.org/mailman/listinfo/python-list
> >
> >Could you please elucidate with a sample script.
> >Suppose I need to pass the switch "-w" to the
> >dynamically loaded code (using eval()/exec()).
> >Any help is appreciated.
> >
> >-Premshree
> >
> 
> What do you mean by a parameter switch?  You mean a
> command-line switch?
> 
> If this is what you mean, it seems you're mixing
> concepts.  If you run the
> Python program as an external program, just do so
> using os.system or
> os.popen or such--the fact that it's written in
> Python makes no difference,
> and exec/execfile is not involved. os.system('python
> mypythonprg -w'), for
> example.
> 
> If you want to have Python code from one program
> exposed to another, the
> best approach is to write a module which can be used
> either as a library or
> a stand-alone program.  The idiom is to put
> something like this:
> 
> if __name__ == '__main__': main()
> 
> at the bottom of your code.  When you run this file
> alone, main() will be
> executed; if you import the file, it won't be.
> 
> If you really need to execute external Python code
> internally (and it's very
> rare and special circumstances where you'd want to),
> use execfile().
> 
> Now, if you're using execfile, it is unlikely that
> the code you're running
> would use command line switches--this implies that
> it's a stand-alone
> program, in which case you should either be running
> it externally (as in
> first solution above) or importing it, and providing
> a mechanism to use it
> programmatically.  This is why I say you seem to be
> mixing concepts.
> 
> That said, command line arguments are available via
> sys.argv, and this is
> most likely how the external program accesses them. 
> You can modify sys.argv
> before execfile().
> 
> This, however, is a mess, because you clobber the
> global sys.argv of the
> original program.  You need to somehow redirect any
> access to sys.argv by
> the script.  You can do so like this:
> 
> >>> sys.argv
> ['']
> >>> class ShadowObject(object):
> ...     def __init__(self, shadowed, **override):
> ...         """Shadow attr access to shadowed with
> override."""
> ...         self.__dict__.update(override)
> ...         self.shadowed = shadowed
> ...     def __getattr__(self, attr):
> ...         """Called only if attr was not in
> override."""
> ...         return getattr(self.shadowed, attr)
> ...
> >>> exec '''print sys.argv          #We get the
> right one?
> ... print sys.getdefaultencoding()  #Make sure we're
> shadowing.
> ... sys.argv = sys.argv[-1:]        #Test
> reassignments.
> ... print sys.argv
> ... ''' in globals(), {'sys':ShadowObject(sys,
> argv=['progname','-w'])}
> ['progname', '-w']
> latin-1
> ['-w']
> >>> sys.argv # the real sys.argv is unchanged
> ['']
> 
> Don't do this.  It's almost certainly not the best
> way to do what you want.
> Why don't you tell us your broader task, and maybe
> we can suggest something
> more Pythonic?
> --
> Francis Avila
> 
> -- 
> http://mail.python.org/mailman/listinfo/python-list 

Hmm...maybe I should have been clearer.
What I need to do is run an external Python code from
within another program, and while doing so I need to
pas a switch (yes, like a command-line switch) to this
code; i.e., I need to open an external Py program from
within another Py program...

Hope I'm clear this time around...

-Premshree

________________________________________________________________________
Yahoo! India Mobile: Download the latest polyphonic ringtones.
Go to http://in.mobile.yahoo.com
More information about the Python-list mailing list