[Python] Solving symbolic sum with symbolic bounds and variables

Given the following sample, I'd expect sympy to find that Sum_x = 30, but for some reason this symbol is not expanded at all in the solution

from sympy import *
from sympy.abc import i

# Symbols
x = IndexedBase('x')
sum_x = Symbol("Sum_x")
sym_bound = Symbol("upper_bound")

concrete_bound = 5
x_constraints = [Eq(x[idx], idx**2) for idx in range(concrete_bound)]

sym_bound_eq = Eq(sym_bound, 5)
equation = Eq(sum_x, Sum(x, (i, 0, sym_bound - 1)).doit())

solution = solve(x_constraints + [equation, sym_bound_eq])
print(solution)


Output:

{Sum_x: Sum(x, (i, 0, upper_bound - 1)), upper_bound: 5, x[0]: 0, x[1]: 1, x[2]: 4, x[3]: 9, x[4]: 16}


How to make it expanded ? (Notes: ideally I'd like to avoid substituting sym_bound with its value, and the expressions of x's are not that simple in my real case)

I got it expanded with this, but it seems verbose and manual:

print(solution[sum_x]
.subs(sym_bound, solution[sym_bound])
.doit()
.subs([(x, solution[x]) for i in range(solution[sym_bound])]))

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