python double colon with -1 as third parameter : <p>Take <code>a = [1,2,3,4,5]</code> as an example. From my instinct, I think <code>a[::-1]</code> is the same as <code>a[0:len(a):-1]</code>. But the result turns to be wrong:</p>

<pre><code>&gt;&gt;&gt; a = [1,2,3,4,5]
&gt;&gt;&gt; print a[::-1]
[5, 4, 3, 2, 1]
&gt;&gt;&gt; print a[0:len(a):-1]
[]
&gt;&gt;&gt; print a[0:3:-1]
[]
&gt;&gt;&gt; print a[0:2:-1]
[]
&gt;&gt;&gt; print a[:2:-1]
[5, 4]
&gt;&gt;&gt; print a[:0:-1]
[5, 4, 3, 2]
&gt;&gt;&gt; print a[0:-1]
[1, 2, 3, 4]
</code></pre>

<p>I actually can't understand the last 6 attempt's output. Could anyone give me some idea? Thanks tons.</p>
