Sorry if this is a stupid question but I tried writing the rmse() function myself in a python REPL and I get an error when I call it:

‘float’ object has no attribute ‘mean’

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from statistics import mean

a = 33.8

b = 129.8

def rmse(x,y): return math.sqrt(((x-y)**2).mean())

rmse(a,b)

…

AttributeError: ‘float’ object has no attribute 'mean

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In the lecture the function works fine. How is mean() being applied to the result of (x-y)**2

if I pass a , b directly to mean() it works fine i,e;

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mean([a,b]) --> 81.8

mean((a,b)) --> 81.8

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