Python Subclassing list

class Mylist(list):

    def __getitem__(self, item):
        print "mygetitem called with", item
        # check if item is slice (l[a:b:c]) or not (l[a])
        if isinstance(item, slice):  # item is slice, check if negative start or stop
            if item.start < 0 or item.stop < 0:
                raise ValueError("negative indexing not supported")
            else:
                return list.__getitem__(self, item)
        else:  # item is single index, check if its negative
            if item < 0:
                raise ValueError("negative indexing not supported")
            else:
                return list.__getitem__(self, item)

    # it seems for getslice, python automatically adjusts start and stop values
    # if they are negative it adds len to it that way we don't receive negative values
    # when called like l[0:-1], we receive l[0:len(l)-1]
    def __getslice__(self, start, stop):
        print "mygetslice called with", start, stop
        return list.__getslice__(self, start, stop)


l = Mylist((1,2,3)) # or l = Mylist(range(10))
print l[0]
print l[5]
print l[-1] # error
print l[0:5]
print l[0:-1] # no error in Python2
print l[0:5:1]
print l[0:-1:1] # error