def _eval_expand_func(self, **hints):
        """
        Function to expand binomial(n,k) when m is positive integer
        Also,
        n is self.args[0] and k is self.args[1] while using binomial(n, k)
        """
        n = self.args[0]
        if n.is_Number:
            return binomial(*self.args)

        k = self.args[1]
        if k.is_Add and n in k.args:
            k = n - k

        if k.is_Integer:
            if k == S.Zero:
                return S.One
            elif k < 0:
                return S.Zero
            else:
                n = self.args[0]
                result = n - k + 1
                for i in range(2, k + 1):
                    result *= n - k + i
                    result /= i
                return result
        else:
            return binomial(*self.args)
dataset/ETHPy150Open sympy/sympy/sympy/functions/combinatorial/factorials.py/binomial._eval_expand_func/original