title: Refresh a list content with another list in Python
body: <p>How would I extend the content of a given list with another given list without using the method <code>.extend()</code>? I imagine that I could use something with dictionaries. </p>
  
  <p><strong>Code</strong></p>
  
  <pre><code>&gt;&gt;&gt; tags  =['N','O','S','Cl']
  &gt;&gt;&gt; itags =[1,2,4,3]
  
  &gt;&gt;&gt; anew =['N','H']
  &gt;&gt;&gt; inew =[2,5]
  </code></pre>
  
  <p>I need a function which returns the refreshed lists </p>
  
  <pre><code>tags  =['N','O','S','Cl','H'] 
  itags =[3,2,4,3,5]
  </code></pre>
  
  <p>When an element is already in the list, the number in the other list is added. If I use the <code>extend()</code> method, the the element <code>N</code> will appear in list <code>tags</code> twice:</p>
  
  <pre><code>&gt;&gt;&gt; tags.extend(anew)
  &gt;&gt;&gt;itags.extend(inew)
  &gt;&gt;&gt; print tags,itags
       ['N','O','S','Cl','N','H'] [1,2,4,3,5,2,5]
  </code></pre>