def moment(X, n, c=0, condition=None, **kwargs):
    return expectation((X - c)**n, condition, **kwargs)
required node attribute properly raise on render
dataset/ETHPy150Open sympy/sympy/sympy/stats/rv_interface.py/moment--crossover with--dataset/ETHPy150Open icook/yota/src/yota/tests/test_nodes.py/TestNode.test_required