title: Get the 1-norm of a vector in Python
body: <p>How can I calculate the 1-norm of the difference of two vectors, <code>||a - b||_1 = sum(|a_i - b_i|)</code> in Python?</p>
  
  <pre><code>a = [1,2,3,4]  
  b = [2,3,4,5]
  
  ||a - b||_1 = 4  
  </code></pre>