Subclassing int for a revolving control number

[Chris Cioffi]

Hello all!

I'm trying to subclass int such that once it reaches a certain value,
it flips back to the starting count. This is for use as an X12
control number. Subclassing int and getting the display like I want
it was trivial, however what's the best way to make it such that:
990 + 1 = 991
991 + 1 = 992
....
998 + 1 = 999
999 + 1 = 001

Should I set any of the special functions like __sub__ to raise
NotImpemented and just make my own custom assignment and __add__
functions? (The other fucntions would make no sense in this
context...)

Is there an "on change" kind of meta-function? (Like the onChange
event in a GUI text control)

Chris
--
Still searching for an even prime > 2!

[Matteo Dell'Amico]

Stephen Ferg wrote:

I think the simplest solution would be just to use a generator...

*************** *************** ******
def rollover(argMax Number=20):
while True:
for i in range(1, argMaxNumber+1) :
yield i

This can also be spelled as itertools.cycle (xrange(max_num ber)).

--
Ciao,
Matteo

[Christopher T King]

On Tue, 20 Jul 2004, Matteo Dell'Amico wrote:

Stephen Ferg wrote:

I think the simplest solution would be just to use a generator...

*************** *************** ******
def rollover(argMax Number=20):
while True:
for i in range(1, argMaxNumber+1) :
yield i

This can also be spelled as itertools.cycle (xrange(max_num ber)).

Watch out: itertools.cycle doesn't restart the generator when it's
exhausted; instead, it keeps a copy of all the items returned by the
iterator and loops over them.

[Calvin Spealman]

Personally, rather than all these suggestions of python-written classes or
of itertools.cycle , I would like a C-extension module with something like
this. All it would have to be is an actually C int value with no bounds
checking. This would be usually for working with low-level data, like
bitmaps or compressed data, where you can't have longs and where you need
good performance on simple arithmetic.

[Christopher T King]

On Tue, 20 Jul 2004, Calvin Spealman wrote:

Personally, rather than all these suggestions of python-written classes or
of itertools.cycle , I would like a C-extension module with something like
this. All it would have to be is an actually C int value with no bounds
checking. This would be usually for working with low-level data, like
bitmaps or compressed data, where you can't have longs and where you need
good performance on simple arithmetic.

numarray does this:

from numarray import *
array(254,UInt8 )+4

2

It also greatly speeds up performance on the vector operations needed in
processing bitmaps, etc.