Re: Sorting a list of objects by multiple attributes
Raymond Hettinger wrote: The cult of lambda avoidance has lost contact with reality. [...] Lambda avoidance is rooted in two things, an aversion to the keyword name [...] Let's push the diagnosis a bit further : the aversion to the keyword lambda has to do with the fact that it ignores the english word used by all non-geeks to convey the meaning, eg given -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
Azolex: Let's push the diagnosis a bit further : the aversion to the keyword lambda has to do with the fact that it ignores the english word used by all non-geeks to convey the meaning, eg given Right. However, Guido has said that lambda is here to stay, so it's time to get over it. Raymond -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
[Noah] I suggested the above because it wasn't obvious to me how one would pass the arbitrary set of attributes to the lambda expression (and I envisioned them being specified as strings in this case, since the set of attributes will be coming from a web form). So what about the following (attrgetter aside)? attrs = 'attr1 attr2 attr3'.split() L.sort(key=lambda i: [getattr(i,a) for a in attrs]) When starting with attribute names in a list of strings, this code looks fine. The Py2.5 version of attrgetter will be even cleaner: L.sort(key=attrgetter(*attrs)) -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
Raymond Hettinger wrote: Azolex: Let's push the diagnosis a bit further : the aversion to the keyword lambda has to do with the fact that it ignores the english word used by all non-geeks to convey the meaning, eg given Right. However, Guido has said that lambda is here to stay, so it's time to get over it. You are saying lambda is a given ? ;) I've not observed the BDFL's pronouncement, so I have to ask : was it clear from his words that he meant the actual keyword, or could it be he just meant the construct while refering to it by the keyword ? -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
gry@ll.mit.edu wrote:
For multiple keys the form is quite analogous:
L.sort(key=lambda i: (i.whatever, i.someother, i.anotherkey))
I.e., just return a tuple with the keys in order from your lambda.
Such tuples sort nicely.
In Python 2.5 you can do this with operator.attrgetter():
L.sort(key=operator.attrgetter('whatever', 'someother', 'anotherkey'))
Kent
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Re: Sorting a list of objects by multiple attributes
Kent Johnson wrote:
In Python 2.5 you can do this with operator.attrgetter():
L.sort(key=operator.attrgetter('whatever', 'someother', 'anotherkey'))
Note: this is also available in Python 2.4
--Scott David Daniels
[EMAIL PROTECTED]
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Re: Sorting a list of objects by multiple attributes
Scott David Daniels wrote:
Kent Johnson wrote:
In Python 2.5 you can do this with operator.attrgetter():
L.sort(key=operator.attrgetter('whatever', 'someother', 'anotherkey'))
Note: this is also available in Python 2.4
No, the ability to specify more than one attribute name, making a getter
that returns a tuple, is a Python 2.5 enhancement. In 2.4:
In [1]: import operator
In [2]: operator.attrgetter('whatever', 'someother', 'anotherkey')
Traceback (most recent call last):
File ipython console, line 1, in ?
TypeError: attrgetter expected 1 arguments, got 3
Kent
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Re: Sorting a list of objects by multiple attributes
[George Young] For multiple keys the form is quite analogous: L.sort(key=lambda i: (i.whatever, i.someother, i.anotherkey)) [Noah] If you are lambda-phobic (as I am) this should also work for an arbitrary set of attributes: attrs = 'attr1 attr2 attr3'.split() sortlist = [[getattr(o,a) for a in attrs] + [o] for o in objects] sorted_objects = [x[-1] for x in sorted(sortlist)] The cult of lambda avoidance has lost contact with reality. Some Pythonistas now habitually twist their code into knots rather than use lambda. The above code fragment is a case in point -- it is shocking that the poster deems the three-line rewrite as an improvement on George's clear and succinct code fragment. Lambda avoidance is rooted in two things, an aversion to the keyword name and an observation that misuse can result in atrocious code. Also, some of the use cases have fallen by the wayside with the introduction of listcomps, genexps, and operator.attrgetter. Still, some use cases remain and there is no reason to mangle your code in the name of a foolish psuedo-principle. My advice: use lambda when appropriate and don't feel guilty about it -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
Kent Johnson wrote:
Scott David Daniels wrote:
Kent Johnson wrote:
In Python 2.5 you can do this with operator.attrgetter():
L.sort(key=operator.attrgetter('whatever', 'someother', 'anotherkey'))
Note: this is also available in Python 2.4
No, the ability to specify more than one attribute name, making a getter
that returns a tuple, is a Python 2.5 enhancement.
Yup, sorry about that. When I installed 2.5a1 the shortcuts I used for
2.4 got switched w/o my noticing (I did try it first). I have now made
my 2.4 shortcuts more explicit (so the next time I'll do this stupid
thing is likely on 2.6).
--
-Scott David Daniels
[EMAIL PROTECTED]
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Re: Sorting a list of objects by multiple attributes
I'm sure my avoidance of lambdas as due as much to laziness as adherence to principle. This is a good opportunity to learn about them. I suggested the above because it wasn't obvious to me how one would pass the arbitrary set of attributes to the lambda expression (and I envisioned them being specified as strings in this case, since the set of attributes will be coming from a web form). So what about the following (attrgetter aside)? attrs = 'attr1 attr2 attr3'.split() L.sort(key=lambda i: [getattr(i,a) for a in attrs]) -Noah -- http://mail.python.org/mailman/listinfo/python-list
Sorting a list of objects by multiple attributes
Hi, I am trying to come up with a clean and simple way to sort a list of objects (in this case SQLObject instances) by multiple attributes. e.g. a Person object may have an age, a lastName, and a firstName. I'd like to be able to arbitrarily sort by any combination of those in any order. I would especially like it to be clear and simple, since I am converting a web app from using SQL to using an ORM only and so the sorting will actually be controlled by variables coming from SELECTs in a web form. In SQL this is easy enough to accomplish, and I can do it in python with L.sort(key=lambda i: i.whatever). But for the multiple attribute case, I'm at a bit of a loss. Thanks for any help. -Steve -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
For multiple keys the form is quite analogous: L.sort(key=lambda i: (i.whatever, i.someother, i.anotherkey)) I.e., just return a tuple with the keys in order from your lambda. Such tuples sort nicely. -- George Young -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a list of objects by multiple attributes
If you are lambda-phobic (as I am) this should also work for an arbitrary set of attributes: attrs = 'attr1 attr2 attr3'.split() sortlist = [[getattr(o,a) for a in attrs] + [o] for o in objects] sorted_objects = [x[-1] for x in sorted(sortlist)] -Noah -- http://mail.python.org/mailman/listinfo/python-list
