Tim Peters wrote:
>
> [Greg Ewing]
>
>>often
>>one wants to sort a collection of objects having
>>keys that can take on null values.
>
> Perhaps that's often true of your code, but it's never been true of mine.
It's fairly common in accounting circles. I have a
collection of invoices, each of which can have a due
date specified, but doesn't have to. I want to sort
the invoices by due date. It's not particularly
important whether the missing dates sort first or
last, but it *is* important that the sort *not blow
up*.
Dates seem to be a particularly irksome case. Here's
one suggestion from StackOverflow for dealing with
the problem:
import datetime
mindate = datetime.date(datetime.MINYEAR, 1, 1)
def getaccountingdate(x):
return x['accountingdate'] or mindate
results = sorted(data, key=getaccountingdate)
That's a ridiculous amount of boilerplate for doing
something that ought to be straightforward.
If you don't want to touch comparison in general,
how about an option to sort()?
results = sorted(invoices, key=attrgetter('duedate'), none='first')
> I have a hard time
> imagining why I'd _want_ to sort a list of objects with "null or
> missing" keys, instead of filtering such garbage out of the list first
A piece of data is *not* garbage just because an optional
part of it is not specified.
--
Greg
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