Sum of q_binomial [closed]

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Hi,

I'm new to sagemath. I'm trying to define a function that depends on a sum of a q-binomial, but I get "unable to convert n to an integer".

So, this works: sum(binomial(n,k),k,1,n)

(output gives $2^n-1$)

but this doesn't: sum(q_binomial(n,k),k,1,n)

All I did was add the "q_", which is the proper way to define a q-binomial in sage, as I already tested (try q_binomial(5,3) and the output is correct).

Anyone can help?