code: def __init__(self, feature, period):
      super().__init__(feature)
      self.period = 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 1 to create a new PRef object from inherited base class: P with example: obj = PRef(feature, period)