code: def variance(arg, where=None, how='sample'):
      
      expr = ops.Variance(arg, how, where).to_expr()
      expr = expr.name('var')
      return expr
docs: Compute standard deviation of numeric array
  
      Parameters
      ----------
      how : {'sample', 'pop'}, default 'sample'
  
      Returns
      -------
      stdev : double scalar