Indentifying the LAST occurrence of an item in a list

[John Machin]

On Apr 7, 9:25 am, "mkPyVS" <mikemine... at hotmail.com> wrote:
> On Apr 5, 6:37 pm, "John Machin" <sjmac... at lexicon.net> wrote:
>
> >>> help(list.index)
> > Help on method_descriptor:
>
> > index(...)
> >     L.index(value, [start, [stop]]) -> integer -- return first index
> > of value
>
> > I look forward to your next version.
>
> Great point! I was assuming the temp variable space was static but the
> pointer to the start of the list was moving-> shame on me (what
> language is this now ;)!

Indeed. IMHO every function/method that searches a sequence should
have start/stop arguments so that the caller can search a slice
without actually copying the slice.

>
> Couldn't resist the temptation to just collect all of the locations as
> I traversed
>
> m = [2,9,1,5,6,3,1,1,9,2]
> f = 1        #What we're looking for
> location = 0 #Start at beginning of list
> fIndexs = []
> while 1:
>    try:
>       location = m.index(f,location) + 1
>       fIndexs.append(location-1)
>    except ValueError:
>       break
>
> print("Last location = %d" % fIndexs[-1])

1. print is a statement, not a function.
2. fIndexs[-1] will crash and burn if there are no occurrences of f in
m.

> print("All Items = %s" % fIndexs)

FWIW, here's my take on a function that emulates the "missing" rindex
method:
8<--- start rindex.py ---
def rindex(seq, value, lo=0, hi=None):
    """If there is an x such that seq[x] == value and lo <= x < hi
    return the largest such x, else raise ValueError"""
    seqlen = len(seq)
    if lo < 0:
        lo += seqlen
        if lo < 0:
            lo = 0
    if hi is None:
        hi = seqlen
    elif hi < 0:
        hi += seqlen
        if hi < 0:
            hi = 0
    lo = seq.index(value, lo, hi)
    while True:
        try:
            lo = seq.index(value, lo + 1, hi)
        except ValueError:
            return lo

if __name__ == "__main__":
    import sys
    av = sys.argv
    print rindex(av[4:], av[1], int(av[2]), int(av[3]))
8<--- end rindex.py ---
Cheers,
John