I know that a[end:start:-1] slices a list in a reverse order.
For example
a = range(20)
print a[15:10:-1] # prints [15, ..., 11]
print a[15:0:-1] # prints [15, ..., 1]
but you cannot get to the first element (0 in the example). It seems that -1 is a special value.
print a[15:-1:-1] # prints []
Any ideas?