zip gets "exhausted" by one loop
<p>when I run python script, a weird output confused me, here is the core test-code:</p>

<pre><code>a = [1,2,3]
b = [4,5,6]
c = zip(a,b)
for i in range(2):
    for x,y in c:
        print(i,x,y)
</code></pre>

<p>only output: </p>

<pre><code>0 1 4
0 2 5
0 3 6
</code></pre>

<p>I was expecting to see results starting with <code>i = 1</code> as well.</p>