title: How do I create an empty array and then append to it in NumPy?
body: <p>I want to create an empty array and append items to it, one  at a time.</p>
  <pre><code>xs = []
  for item in data:
      xs.append(item)
  </code></pre>
  <p>Can I use this list-style notation with <a href="http://en.wikipedia.org/wiki/NumPy" rel="noreferrer">NumPy</a> arrays?</p>