title: Why is the list.copy() method shallow?
body: <p>In the official Python documentation said that list.copy() returns a shallow copy of the list.
  But according to the following code it is deep copy since the change of one list does not lead to the change in another.</p>
  <pre><code>&gt;&gt;&gt; num1 = [1,2,3,4,5]
  &gt;&gt;&gt; num2 = num1.copy()
  &gt;&gt;&gt; num1.append(9)
  &gt;&gt;&gt; num1
  [1, 2, 3, 4, 5, 9]
  &gt;&gt;&gt; num2
  [1, 2, 3, 4, 5]
  </code></pre>
  <p>What is the problem? Where is a mistake?</p>