title: Run 3 python functions concurrently then add their values together
body: <p>I am generating the coefficients for x, y and z. I want to run the generating functions simultaneously (as they take a while), then once all generated, merge the coefficients together. My ideal code will be a bit like this:</p>
  <pre><code>#generated in parallel
    x = generate_x()
    y = generate_y()
    z = generate_z()
  
  merged = x + y + z
  </code></pre>
  <p>I don't want to wait for each generate function before I start generating the next one, but I also need them all to finish before I merge them at the end. How can this be done?</p>