title: I made a copy of the list but when I make a change to the copy, the original list still changes. I don't understand why
body: <pre><code>l = [[1, 2, 3], [1, 2, 3, 5], [5, 6, 8]]
  p = l.copy()
  for indx, value in enumerate(p):
      del value[0]
  print(l)
  print(p)
  </code></pre>
  
  <p>Output: [[2, 3], [2, 3, 5], [6, 8]]<br>
          [[2, 3], [2, 3, 5], [6, 8]] </p>