Python vertical stack not working
Since X is a numpy array, you can do X.shape instead of the repeated len.  I expect it to show (13934, 74).
I expect Y.shape to be (13934,). It's a 1d array, which is why Y[0] is a number, numpy.int64.  And since it is 1d, transpose (swapping axes) doesn't do anything.  (this isn't MATLAB where everything has at least 2 dimensions.)
It looks like you want to create an array that has shape (13934, 75).  To do that you'll need to add a dimension to Y.  Y[:,None] is a concise way of doing that.  The shape of that is (13934,1), which will concatenate with X.  If that None syntax is puzzling, try, Y.reshape(-1,1) (or reshape(13934,1)).
I have a matrix X which has len(X) equal to 13934 and len(X[i]), for all i, equal to 74, and I have an array Y which has len(Y) equal to 13934 and len(Y[i]) equal to TypeError: object of type 'numpy.int64' has no len() for all i.
When I try np.vstack((X,Y)) or result = np.concatenate((X, Y.T), axis=1)
I get ValueError: all the input array dimensions except for the concatenation axis must match exactly
What is the problem?
When I print out Y it says array([1,...], dtype=int64) and when I print out X it says array([data..]) with no dtype. Could this be the problem?
I tried converting them both to float32 by doing X.view('float32') and this did not help.