Solved by ptrblck in post #4 
              
              
                Assuming this numpy array is stored locally as an npy file, you could use np.load with the mmap_mode, which would allow you to load sliced from the disc without reading the whole array into memory: 

mmap_mode {None, ‘r+’, ‘r’, ‘w+’, ‘c’}, optional 
If not None, then memory-map the file, using the g…