catching exceptions from fortran

[john]

On Sep 11, 8:23 pm, "Gabriel Genellina" <gagsl-... at yahoo.com.ar>
wrote:
> En Thu, 11 Sep 2008 10:43:08 -0300, john <john.m.ro... at gmail.com> escribió:
>
>
>
>
>
> > I wrapped some fortran code using F2PY and need to be able to catch
> > fortran runtime errors to run the following:
>
> [reindented]
> > # "grid" is a wrapped fortran module
> > # no runtime errors incurred when run with the correct inputs for
> > filetype
> > #-------------------------------
> > def readGrid( self, coord='xyz' ):
> >   mg = ( '.FALSE.', '.TRUE.' )
> >   form = ( 'FORMATTED', 'UNFORMATTED' )
> >   success = False
> >   for m in mg:
> >     for f in form:
> >       try:
> >         if coord == 'xyz':
> >           self.grid.readxyz( self.filename, f, m )
> >           success = True
> >         elif coord == 'xyrb':
> >           self.grid.readxyrb( self.filename, f, m )
> >           success = True
> >         else:
> >           import sys
> >           print 'gridtype "' + str(coord) + '" not supported. ' \
> >               + '<IO.Plot3d.Plot3d.read>'
> >       except:
> >         continue
> >   if not success:
> >     import sys
> >     print 'gridfile "' + str(self.filename) + '" not read in any  
> > recognized format' \
> >         + ' <IO.Plot3d.Plot3d.read>'
> > #----------------------------
>
> I suppose you want to stop trying other formats after a successful read;  
> in that case put a break statement just below both success=True.
> If coord is unrecognized, the code above prints the same message 4 times.  
> Instead of printing a message, in those cases usually an exception is  
> raised, letting a higher layer handle the error. And using string  
> interpolation is a lot easier than building the message in parts:
> raise ValueError('gridtype "%s" not supported. <IO.Plot3d.Plot3d.read>' %  
> coord)
> If you want to catch errors on the Fortran code *only*, the try/except  
> should be more specific (both in scope and what it catches). The Exception  
> class is the more generic exception that you should catch.
>
> > basically, what i want to happen is to try to run 'something' with the
> > wrapped fortran code and if that doesn't work (error encountered,
> > etc.) try something else.  is there an easier way to go about doing
> > this?  is there something i'm missing about catching exceptions here?
>
> I'd reorder the code in this way (untested, of course):
>
> def readGrid(self, coord='xyz'):
>
>      def try_all_formats(read_function, filename):
>          mg = ('.FALSE.', '.TRUE.')
>          form = ('FORMATTED', 'UNFORMATTED')
>          success = False
>          for m in mg:
>              for f in form:
>                  try:
>                      read_function(filename, f, m)
>                      success = True
>                      break
>                  except Exception, e:
>                      # this line only for debugging purposes
>                      print "error %r when using m=%r f=%r" % (e, m, f)
>                      continue
>          if not success:
>              raise ValueError('gridfile "%s" not read '
>                     'in any recognized format '
>                     '<IO.Plot3d.Plot3d.read>' % filename)
>
>      if coord == 'xyz':
>          try_all_formats(self.grid.readxyz, self.filename)
>      elif coord == 'xyrb':
>          try_all_formats(self.grid.readxyrb, self.filename)
>      else:
>          raise ValueError('gridtype "%s" not supported. '
>                  '<IO.Plot3d.Plot3d.read>' % coord)
>
> I don't know about F2PY but the values ('.FALSE.', '.TRUE.') seem  
> suspicious. AFAIR, .FALSE. and .TRUE. are the Fortran spellings of False  
> and True in Python - they're not strings, but boolean values. So maybe the  
> right way is to use
>          mg = (False, True)
>
> Your code above was catching and ignoring everything, even this error, if  
> it happened.
>
> --
> Gabriel Genellina

Gabriel,

i agree with everything you write, but unless i misunderstood
something, this still doesn't address the main problem of the try-
except construct not preventing the program from aborting when the
wrapped fortran code encounters an error.  i tried hard-coding all of
the passed variables to the fortran code and ran that code alone--
works.  however, when an incorrect fortran read is attempted (ex.
formatted read on unformatted file), the python except still fails to
catch the error and the code aborts with a runtime error...