class_docstr: Base callback class.
  
  .. note::
  
      All callbacks should override this class.
class_docstr_tok: ["Base","callback","class",".","..","note",":",":","All","callbacks","should","override","this","class","."]
code: def __str__(self):
      return (
          str(self.__class__)
          .replace("<class ", "")
          .replace(">", "")
          .replace("'", "")
      )
  
imports: import functools
  import traceback
  import warnings
  import torch
  from packaging import version
  import torchbearer
  import sys
label_desc: Use image node_id 2 for calling the Callback obj's underlying member method code with example usage: obj.__str__() and returns: str