title: Visibility in a function
body: <p>I have this code:</p>
  
  <pre><code>def h(l1,l2):
      l1.pop()
      l2 = l2 +l1
  
  
  
  l1=[1,2,3]
  l2=[]
  h(l1,l2)
  print (l1,l2)
  </code></pre>
  
  <p>Why after running the code, l1 is  [1,2]  and l2 remain the same ([]).Why l2 is not [1,2]?</p>