code: def get_reduction_callable(cls, op):
      skipna, ddof = op.skipna, op.ddof
  
      def var(x):
          cnt = x.count()
          if ddof == 0:
              return (x**2).mean(skipna=skipna) - (
                  x.mean(skipna=skipna)
              ) ** 2
          return (
              (x**2).sum(skipna=skipna)
              - x.sum(skipna=skipna) ** 2 / cnt
          ) / (cnt - ddof)
  
      return var
  
file_path: mars/mars/dataframe/reduction/var.py
imports: from ...None import opcodes
  from ...config import options
  from ...core import OutputType
  from ...serialization.serializables import Int32Field
  from .core import DataFrameReductionOperand, DataFrameReductionMixin
label_desc: Use image node_id 3 for calling the DataFrameVar obj's underlying member method code with example usage: obj.get_reduction_callable(cls, op) and returns: var, unknown, unknown