title: appending numpy arrays to python list overwrites existing elements in list
body: <p>I am trying to get a python list of numpy arrays, by appending to an initially empty list in a loop. The problem is this: the new array to be added is computed correctly, the list gets expanded by this new element but every element in the list gets overwritten with this new element.
  Here is the code:</p>
  
  <pre><code>from numpy import *
  
  pos = array([0., 0, 0])
  vel = array([1., 0, 0])
  t, tf, dt = 0., 1, 0.1
  ppos = [pos]
  while t &lt; tf:
      pos += vel*dt
      ppos.append(pos) 
      t += dt
  </code></pre>
  
  <p>Thanks</p>