code: def center(self):
      return self._center
  
imports: from collections import namedtuple
  from functools import partial
  import numpy
  import pandas
  from ....None import opcodes
  from ....serialization.serializables import BoolField
  from ..aggregation import BaseDataFrameExpandingAgg
label_desc: Use image node_id 2 for calling the DataFrameExpandingAgg obj's underlying member method code with example usage: obj.center() and returns: self