Dedekind eta function in sage

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I would like to use the dedekind eta function, $q^{\frac{1}{24}}\prod_{n=1}(1-q^n)$, in my code. However when I do

N = 20
R.<q> = PowerSeriesRing(QQ,default_prec=p*N+1)

eta = q^(1/24) * prod([(1-q^n) for n in range(1,N)]) 
eta = R(eta.truncate(N))

I get "ValueError: power series valuation is not a multiple of 24". I would like to know how I can implement the formula above or if there is some inbuilt eta function I can use somehow (I couldn't find anything in the documentation).