Implementing python slice notation

Question

I\'m trying to reimplement python slice notation in another language (php) and looking for a snippet (in any language or pseudocode) that would mimic the python logic. That is,

Answer 1

Here's a straight port of the C code:

def adjust_endpoint(length, endpoint, step):
     if endpoint < 0:
         endpoint += length
         if endpoint < 0:
             endpoint = -1 if step < 0 else 0
     elif endpoint >= length:
         endpoint = length - 1 if step < 0 else length
     return endpoint

def adjust_slice(length, start, stop, step):
     if step is None:
         step = 1
     elif step == 0:
         raise ValueError("step cannot be 0")

     if start is None:
         start = length - 1 if step < 0 else 0
     else:
         start = adjust_endpoint(length, start, step)

     if stop is None:
         stop = -1 if step < 0 else length
     else:
         stop = adjust_endpoint(length, stop, step)

     return start, stop, step

def slice_indices(length, start, stop, step):
     start, stop, step = adjust_slice(length, start, stop, step)
     i = start
     while (i > stop) if step < 0 else (i < stop):
         yield i
         i += step

def mySlice(L, start=None, stop=None, step=None):
     return [L[i] for i in slice_indices(len(L), start, stop, step)]