class_docstr: Trigger a callback every k global steps or every k epochs by its :meth:`trigger()` method.
  
  Most existing callbacks which do something every epoch are implemented
  with :meth:`trigger()` method. By default the :meth:`trigger()` method will be called every epoch.
  This wrapper can make the callback run at a different frequency.
  
  All other methods (``before/after_run``, ``trigger_step``, etc) of the given callback
  are unaffected. They will still be called as-is.
code: def __str__(self):
      return "PeriodicTrigger-" + str(self.cb)
  
imports: from .base import Callback, ProxyCallback
label_desc: Use image node_id 5 for calling the PeriodicTrigger obj's underlying member method code with example usage: obj.__str__() and returns: unknown