docs: def open_by_pat(self, name, mode='r', **kwargs):
          '''
          opens the file for the pattern given by *name*,
          substituting the object's properties and the
          additional keyword arguments given.
          '''
          fname = self.fname_by_pat(name, **kwargs)
          if mode == 'w':
              print >>sys.stderr, "Write[%s]: %s" % (name, fname)
          else:
              print >>sys.stderr, "Open[%s]: %s" % (name, fname)
          return file(fname, mode)