Type Error Confusion

[Oliver]

X0 = [1,2,3]
X1 = [4,5,6]
k = len(np.cov(X0))

Throws this error:

k = len(np.cov(X0))
TypeError: len() of unsized object

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I tried using an numpy array, but got the same error.

How to get around this problem?

Thanks in advance,

- O