python find smallest value in 2d list

>>> a = [[8,2,3,4,5,6],
... [3,6,6,7,2,6],
... [3,8,5,1,2,9],
... [6,4,2,7,8,3]]
>>> mymin = min([min(r) for r in a])
>>> mymin

Here is what the above code is Doing:
1. a is a list of lists.
2. [min(r) for r in a] is a list comprehension that returns a list of the minimum values of each list in a.
3. mymin = min([min(r) for r in a]) assigns the minimum value of the list comprehension to mymin.
4. mymin