't.open_r(file) and t.open_w(file) implement
t.open(file, \'r\') and t.open(file, \'w\') respectively.'

def open_r(self, file):

    if (not self.steps):
        return open(file, 'r')
    if (self.steps[(-1)][1] == SINK):
        raise ValueError('Template.open_r:    pipeline    ends    width    SINK')
    cmd = self.makepipeline(file, '')
    return os.popen(cmd, 'r')
