What does [[]]*2 do in python?
<pre><code>A = [[]]*2

A[0].append("a")
A[1].append("b")

B = [[], []]

B[0].append("a")
B[1].append("b")

print "A: "+ str(A)
print "B: "+ str(B)
</code></pre>

<p>Yields:</p>

<pre><code>A: [['a', 'b'], ['a', 'b']]
B: [['a'], ['b']]
</code></pre>

<p>One would expect that the A list would be the same as the B list, this is not the case, both append statements were applied to A[0] and A[1].</p>

<p>Why?</p>
