title: Appending to numpy array within a loop
body: <p>I really hope to not have missed something, that had been clarified before, but I couldn't find something here.</p>
  
  <p>The task seems easy, but I fail. I want to continuously append a numpy array to another one while in a for-loop:</p>
  
  <pre><code>step_n = 10
  steps = np.empty([step_n,1])
  
  for n in range(step_n):
      step = np.random.choice([-1, 0, 1], size=(1,2))
      #steps.append(step) -&gt; if would be lists, I would do it like that
      a = np.append(steps,step)
      #something will be checked after each n
  
  print(a)
  </code></pre>
  
  <p>The output should be ofc of type <code>&lt;class 'numpy.ndarray'&gt;</code> and look like:</p>
  
  <pre><code>[[-1.  0.]
   [ 0.  0.]
   [-1. -1.]
   [ 1. -1.]
   [ 1.  1.]
   [ 0. -1.]
   [-1.  1.]
   [-1.  0.]
   [ 0. -1.]
   [ 1.  1.]]
  </code></pre>
  
  <p>However the code fails for some (most probably obvious) reasons. 
  Can someone give me a hint?</p>