Understanding Python s slice notation

Question

I need a good explanation on Python's slice notation.

To me, this notation needs a bit of picking up.

It looks extremely powerful, but I haven't quite got my head around it.

Answer 1

It's pretty simple really:

a[start:end] # items start through end-1
a[start:]    # items start through the rest of the array
a[:end]      # items from the beginning through end-1
a[:]         # a copy of the whole array
There is also the step value, which can be used with any of the above:

a[start:end:step] # start through not past end, by step
The key point to remember is that the :end value represents the first value that is not in the selected slice. So, the difference beween end and start is the number of elements selected.