try-except syntax

[ElChino]

I'm trying to simplify a try-except construct. E.g. how come
this:
   try:
     _x, pathname, _y = imp.find_module (mod, mod_path)
     return ("%s" % pathname)
   except ImportError:
     pass
   except RuntimeError:
     pass
     return ("<unknown>")

Cannot be simplified into this:
   try:
     _x, pathname, _y = imp.find_module (mod, mod_path)
     return ("%s" % pathname)
   except ImportError:
   except RuntimeError:
     pass
     return ("<unknown>")

Like a "fall-through" in a C-switch statement.