class_docstr: A `Callback` to handle the display of progress bars
class_docstr_tok: ["A","`","Callback","`","to","handle","the","display","of","progress","bars"]
code: def before_epoch(self):
      if getattr(self, "mbar", False):
          self.mbar.update(self.epoch)
  
imports: from __future__ import annotations
  from ..basics import *
label_desc: Use image node_id 2 for calling the ProgressCallback obj's underlying member method code with example usage: obj.before_epoch() without return types