Python: Does an iteration through 'list[a:b]' first copy that part of the list (which could be expensive)?
<p>When I iterate through the values of <code>list1</code> from <code>start</code> to <code>stop</code>, as in:</p>

<pre><code>for value in list1[start:stop]:
    ....
</code></pre>

<p>Does python first copy that part of the list (as is done when doing <code>list2 = list1[:]</code>)? This could get  very expensive for large lists!</p>

<p>If it doesn't copy it in the above example, does that always hold true? I need to do the following sort of loop, very often, on large sections of (very) large lists:</p>

<pre><code>for index, value in enumerate(list1[start:stop], start):
    ....
</code></pre>
