==== Intersect lists but preserve the order ====
{tags: intersection without changing order}
<code>
In [1]:
required = ['c', 'b', 'a']; available = ['a', 'b', 'd']
required_and_available = [x for x in required if x in available]

In [2]:
required_and_available
Out[2]:
['b', 'a']
</code>