def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def gradients(self, d_grads, g_grads):
      if self.d_grads is None:
          self.d_grads = [torch.zeros_like(_g) for _g in d_grads]
          self.g_grads = [torch.zeros_like(_g) for _g in g_grads]