numpy concatenate multiple arrays arrays
So, the main problem here was with the one of the arrays of shape (0,) instead of (0,227,227,3). 
np.concatenate(alist,axis=0) works.
I have many numpy arrays of shape (Ni,227,227,3), where Ni of each array is different.
I want to join them and make array of shape (N1+N2+..+Nk,227,227,3) where k is the number of arrays.
I tried numpy.concatenate and numpy.append but they ask for same dimension in axis 0. I am also confused on what is axis 1 and axis 2 in my arrays.