code: def __str__(self):
      return f"{super().__str__()}[{self.period}]"
  
file_path: qlib/qlib/data/pit.py
imports: import numpy
  import pandas
  from qlib.data.ops import ElemOperator
  from qlib.log import get_module_logger
  from .data import Cal
label_desc: Use image node_id 2 for calling the PRef obj's underlying member method code with example usage: obj.__str__() and returns: super, str, self, str