class_docstr: Represent a callback to execute periodically on the ``IOLoop`` at a
  specified periodic time interval.
class_docstr_tok: ["Represent","a","callback","to","execute","periodically","on","the","``","IOLoop","``","at","a","specified","periodic","time","interval","."]
docstr: The period time (in milliseconds) that this callback should
  repeat execution at.
docstr_tok: ["The","period","time","(","in","milliseconds",")","that","this","callback","should","repeat","execution","at","."]
code: def period(self) -> int:
      """The period time (in milliseconds) that this callback should
      repeat execution at.
  
      """
      return self._period
  
imports: from __future__ import annotations
  import logging
  from typing import TYPE_CHECKING, Callable, Sequence
  from ..core.types import ID
  from ..util.tornado import _CallbackGroup
label_desc: Use image node_id 2 for calling the PeriodicCallback obj's underlying member method code with example usage: obj.period() and returns: self