code: def forward(self, input):
      foo = yield stash("foo")
      return input + foo
  
imports: from torch import nn
  from fairscale.nn.pipe.skip import Namespace, pop, skippable, stash
  from fairscale.nn.pipe.skip.layout import inspect_skip_layout
label_desc: Use image node_id 1 for calling the PopFoo obj's underlying member method code with example usage: obj.forward(input) and returns: unknown