title: Multiple names refer to 1 value issue
body: <p>I have read this link recently <a href="https://nedbatchelder.com/text/names.html" rel="nofollow noreferrer">here</a>
  and it raises a question. The author only said about this</p>
  
  <pre><code>x = 23
  y = x
  </code></pre>
  
  <p>But what about this</p>
  
  <pre><code>x = 23
  y = 23
  </code></pre>
  
  <p>Is it still right that both x and y refer to one value 23 ? the first “23” is the same as the second “23” ? If it is then why I try this</p>
  
  <pre><code>a=[1,2,3]
  b=[1,2,3]
  b.reverse()
  print(a)
  </code></pre>
  
  <p>The result is</p>
  
  <pre><code>[1, 2, 3]
  </code></pre>
  
  <p>Why is that? because both a and b refer to value [1,2,3] and list is a mutable type. As the author said 
      "if two names refer to the same value, and the value is mutated, then both names see the change" In my code, b changed, why a didn't</p>