ValueError: cannot convert n to int

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SymPy's product function does transform that particular symbolic product into the factorial:

sage: from sympy import product, symbols
sage: i, n = symbols('i, n')
sage: product(i, (i, 1, n-1))
factorial(n - 1)

It makes me think that for prod it is a feature which hasn't been implemented but perhaps i'm mistaken. Note that sum has a nicer behavior: for instance sum(1/i, i, 1, n) returns harmonic_number(n).

One alternative is not using prod but just factorial(n-1), as already suggested by kcrisman. Another alternative is to define a Python's lambda function (more on this here), as in:

sage: someProduct = lambda n : prod([i for i in range(1, n)])
sage: someProduct(10)
362880

The symbolic product exists somewhere already (probably in Maxima?), so with some trickery you can get something that looks like it:

sage: function("f")
f
sage: var("n")
n
sage: function("f")
f
sage: P=exp(sum(log(f(x)),x,1,n-1)); P
product(f(x), x, 1, n - 1)

At this point, P.operator is just a formal object: sage itself doesn't know anything about it:

sage: product=P.operator()
sage: product(x,x,1,n).simplify_full()
product(x, x, 1, n)

whereas

sage: exp(sum(log(x),x,1,n))
factorial(n)