title: What is the advantage of saving `.npz` files instead of `.npy` in python, regarding speed, memory and look-up?
body: <p>The python documentation for the <code>numpy.savez</code> which saves an <code>.npz</code> file is:</p>
  
  <blockquote>
    <p>The .npz file format is a zipped archive of files named after the variables they contain. The archive is not compressed and each file in the archive contains one variable in .npy format. [...]</p>
    
    <p>When opening the saved .npz file with load a NpzFile object is
    returned. This is a dictionary-like object which can be queried for
    its list of arrays (with the .files attribute), and for the arrays
    themselves.</p>
  </blockquote>
  
  <p>My question is: what is the point of <code>numpy.savez</code>?</p>
  
  <p>Is it just a more elegant version (shorter command) to save multiple arrays, or is there a speed-up in the saving/reading process? Does it occupy less memory?</p>