code: def aggregate(self, func, **kwargs):
      from .aggregation import DataFrameExpandingAgg
  
      count_always_valid = kwargs.pop("_count_always_valid", False)
  
      op = DataFrameExpandingAgg(
          func=func,
          count_always_valid=count_always_valid,
          **self.params,
      )
      return op(self)
  
imports: from collections import OrderedDict
  from ....serialization.serializables import BoolField, Int32Field, Int64Field, StringField
  from ....utils import pd_release_version
  from ...utils import validate_axis
  from ..core import Window
label_desc: Use image node_id 8 for calling the Expanding obj's underlying member method code with example usage: obj.aggregate(func) and returns: op