What is the len of the equivalent nested list?
len([[2,3,1,0], [2,3,1,0], [3,2,1,1]])
With the more general concept of shape, numpy developers choose to implement __len__ as the first dimension. Python maps len(obj) onto obj.__len__.
X.shape returns a tuple, which does have a len - which is the number of dimensions, X.ndim. X.shape[i] selects the ith dimension (a straight forward application of tuple indexing).