code: def get_reduction_callable(cls, op):
      from .aggregation import where_function
  
      skipna, bias = op.skipna, op.bias
  
      def skew(x):
          cnt = x.count()
          mean = x.mean(skipna=skipna)
          divided = (
              (x**3).mean(skipna=skipna)
              - 3 * (x**2).mean(skipna=skipna) * mean
              + 2 * mean**3
          )
          var = x.var(skipna=skipna, ddof=0)
          if isinstance(var, ENTITY_TYPE) or var > 0:
              val = where_function(
                  var > 0, divided / var**1.5, np.nan
              )
          else:
              val = np.nan
          if not bias:
              val = where_function(
                  (var > 0) & (cnt > 2),
                  val * ((cnt * (cnt - 1)) ** 0.5 / (cnt - 2)),
                  np.nan,
              )
          return val
  
      return skew
  
file_path: mars/mars/dataframe/reduction/skew.py
imports: import numpy
  from ...None import opcodes
  from ...config import options
  from ...core import OutputType, ENTITY_TYPE
  from ...serialization.serializables import BoolField
  from .core import DataFrameReductionOperand, DataFrameReductionMixin
label_desc: Use image node_id 3 for calling the DataFrameSkew obj's underlying member method code with example usage: obj.get_reduction_callable(cls, op) and returns: skew, val