opens the file for the pattern given by *name*,
        substituting the object's properties and the
        additional keyword arguments given.

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)