title: Running Cumulative sum of 1d NumPy Array
body: <p>I have a numpy array like  </p>
  
  <p><code>
  x=np.array([1,2,3,4])
  </code></p>
  
  <p>I want to create another numpy array y which is the cumulative sum of x, so that </p>
  
  <p><code>
  y=np.array([1,3,6,10])
  </code></p>
  
  <p>What is a good num-Pythonic way to do this?</p>