Need a strange sort method...

[SpreadTooThin]

I have a list and I need to do a custom sort on it...

for example:
a = [1,2,3,4,5,6,7,8,9,10] #Although not necessarily in order

def cmp(i,j):  #to be defined in this thread.

a.sort(cmp)

print a
[1,4,7,10,  2,5,8, 3,6,9]

So withouth making this into an IQ test.
Its more like
1 4 7 10
2 5 8
3 6 9

Read that top to bottom from column 1 to column 4.
When you get to the bottom of a column move to the next column.
Get it?