Variable in loop on Python don't change : <p>I can't understand why in loop variable don't change, but I explicitly try it. So here is my code:</p>

<pre><code>a=[1,2,3]
b=["a","b","c"]
d=[a,b]
for i in d:
    for a in i:
         a*2
         print(a)
</code></pre>

<p>And when I run I see :</p>

<pre><code>1
2
3
a
b
c
</code></pre>

<p>Instead expected:</p>

<pre><code>2
4
6
aa
bb
cc
</code></pre>
