Sort elements in a list - Python

a = ['S', 'XXL', 'M', 'L' ]
b = ['XS','S','M','L','XL','XXL']
a.sort(key=lambda (x): b.index(x))
print a
>>>['S', 'M', 'L', 'XXL']

K = ['22', '40', '70', '10']
K = sorted(K)
print K
>>>['10', '22', '40', '70']

K = ['22', '40', '70', '10']
K = sorted(K, reverse=True)
print K
>>>['70', '40', '22', '10']