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

I can't say there's no bug in the codes, but it had past your test program :)

def mySlice(L, start=None, stop=None, step=None):
    ret = []
    le = len(L)
    if step is None: step = 1

    if step > 0: #this situation might be easier
        if start is None: 
            start = 0
        else:
            if start < 0: start += le
            if start < 0: start = 0
            if start > le: start = le

        if stop is None: 
            stop = le
        else:
            if stop < 0: stop += le
            if stop < 0: stop = 0
            if stop > le: stop = le
    else:
        if start is None:
            start = le-1
        else:
            if start < 0: start += le
            if start < 0: start = -1
            if start >= le: start = le-1

        if stop is None: 
            stop = -1 #stop is not 0 because we need L[0]
        else:
            if stop < 0: stop += le
            if stop < 0: stop = -1
            if stop >= le: stop = le

    #(stop-start)*step>0 to make sure 2 things: 
    #1: step != 0
    #2: iteration will end
    while start != stop and (stop-start)*step > 0 and start >=0 and start < le:
        ret.append( L[start] )
        start += step

    return ret