Why tuple assignment failed?
<p>I have tried to assign new data to existing tuple, and it does not work.and actually I want to add    the a and b to get a sum, however only string can be iterated..</p>

<pre><code>A=[('3', '4'), ('3', '11'), ('8', '10')] 
  print A
for a,b in A:
  a,b = int(a), int(b)+int(a)
print A
</code></pre>

<p>results:</p>

<p>[('3', '4'), ('3', '11'), ('8', '10')]</p>

<p>[('3', '4'), ('3', '11'), ('8', '10')]</p>
