class_docstr: Holds callbacks that are notified when TensorVariable are used.
class_docstr_tok: ["Holds","callbacks","that","are","notified","when","TensorVariable","are","used","."]
code: def notify(self, variable):
      if self._recording:
          assert isinstance(variable, TensorVariable)
          for callback in self._callbacks:
              callback(variable)
  
imports: import collections
  import functools
  import itertools
  import threading
  import contextlib
  from sonnet.src.functional import utils
  import tensorflow
label_desc: Use image node_id 2 for calling the TensorVariableCallbacks obj's underlying member method code with example usage: obj.notify(variable) without return types