Multiple "cmp"s chained one after another

[vincent wehren]

"Volker Grabsch" <volker_grabsch at v.notjusthosting.com> schrieb im 
Newsbeitrag news:d65h73$fgr$02$2 at news.t-online.com...
| vincent wehren wrote:
| >
| > If you don't care about the year, why not just "normalize" the year
| > to all be the same using the replace method of the date instance?
|
| That's a very bad idea. In my example, this would work, but in "reality"
| I don't sort datetime objects, of course! (Is there any real application
| where you want to do that?)
|
| Instead, I'm sorting "Person" objects using a "birthday" attribute.
| Since I use these Person objects also in other places, they should never
| be modified without just to be sorted. In general, the number side effects
| should always be minimized.

Can you explain where you see a modification to the orginal object 
happening?
(or in any of the other solutions proposed for that matter...)

Not here I hope:

|
| > datesNorm = [obj.replace(year=1900) for obj in (dates)]
| > datesNorm.sort()

If you print datesNorm, you'll see:

[datetime.date(1900, 12, 2), datetime.date(1900, 12, 3), datetime.date(1900, 
12, 6), datetime.date(1900, 12, 7)]

However, dates is still the same:

[datetime.date(2004, 12, 2), datetime.date(2001, 12, 3), datetime.date(2002, 
12, 6), datetime.date(1977, 12, 7)]

|
| This code would go bad especially in my situation, where my "Person"
| objects are SQLObjects, thus the "normalisation" would be written into
| the database. Okay, one could use transactions and rollback", but I
| think, my point is clear now.

Since you wouldn't need to change the attribute object to
perform a sort (on the instances) using it (or portions of it) as key, it's 
not.
Or is there something fundamental I am missing about your particular use 
case?

| Nevertheless, I think you idea is very interesting. Is there any "real"
| application where normalizing just for sorting would be reasonable?

How about a case-insensitive sort of strings? (uppering being the 
normalization step)
Or getting rid of accented / special characters before sorting.
These sound like fairly straight-forward use cases to me ;)

Anyway, I was doing some SQL this morning where getting rid of portions of 
'datetime' fields in
a WHERE clause is sometimes just the ticket - hence the connection.


--

Vincent


|
| -- 
| Volker Grabsch
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