Root Mean Square of a Function in Python

I'm going to assume that you want to compute the expression given by the following pseudocode:

ms = 0
for i = 1 ... N
    ms = ms + y[i]^2
ms = ms / N
rms = sqrt(ms)

i.e. the square root of the mean of the squared values of elements of y.

In numpy, you can simply square y, take its mean and then its square root as follows:

rms = np.sqrt(np.mean(y**2))

So, for example:

>>> y = np.array([0, 0, 1, 1, 0, 1, 0, 1, 1, 1])  # Six 1's
>>> y.size
10
>>> np.mean(y**2)
0.59999999999999998
>>> np.sqrt(np.mean(y**2))
0.7745966692414834

Do clarify your question if you mean to ask something else.