Re: [Tutor] calculating a sort key and operator.attrgetter()

[Kent Johnson]

On Tue, Jun 30, 2009 at 11:39 PM, Vincent Davisvinc...@vincentdavis.net wrote:
 I have a class with an attribute which is a list rank_list this is a list
 of instances f another class that has attributes quality, is_observed
 if I want to sort the list by the attribute quality I can just use,
 self.rank_list.sort(key=operator.attrgetter('quality'))
 But I want to sort like this.
 self.rank_list.sort(key=(operator.attrgetter('quality') *
 operator.attrgetter('is_observed') * self.does_observe))
 Will this work or is there a better way?

That won't work because attrgetter() returns a function and you can't
multiply functions. What you can do is define your own function that
returns the value you want for the key and use that for the sort. I'm
leaving out self.does_observe because that won't change for the list
items, wil it?

def make_key(item):
  return item.quality * item.is_observed

self.rank_list.sort(key=make_key)

Kent
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Re: [Tutor] calculating a sort key and operator.attrgetter()

[Vincent Davis]

Thanks for the help, Looks like I will define a function. And yes you are
right self.does_observe is constant so it will not affect the outcome.

Thanks again
Vincent Davis



On Tue, Jun 30, 2009 at 11:15 PM, Kent Johnson ken...@tds.net wrote:

 On Tue, Jun 30, 2009 at 11:39 PM, Vincent Davisvinc...@vincentdavis.net
 wrote:
  I have a class with an attribute which is a list rank_list this is a
 list
  of instances f another class that has attributes quality, is_observed
  if I want to sort the list by the attribute quality I can just use,
  self.rank_list.sort(key=operator.attrgetter('quality'))
  But I want to sort like this.
  self.rank_list.sort(key=(operator.attrgetter('quality') *
  operator.attrgetter('is_observed') * self.does_observe))
  Will this work or is there a better way?

 That won't work because attrgetter() returns a function and you can't
 multiply functions. What you can do is define your own function that
 returns the value you want for the key and use that for the sort. I'm
 leaving out self.does_observe because that won't change for the list
 items, wil it?

 def make_key(item):
  return item.quality * item.is_observed

 self.rank_list.sort(key=make_key)

 Kent

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[Tutor] calculating a sort key and operator.attrgetter()

[Vincent Davis]

I have a class with an attribute which is a list rank_list this is a list
of instances f another class that has attributes quality, is_observed
if I want to sort the list by the attribute quality I can just use,
self.rank_list.sort(key=operator.attrgetter('quality'))
But I want to sort like this.
self.rank_list.sort(key=(operator.attrgetter('quality') *
operator.attrgetter('is_observed') * self.does_observe))
Will this work or is there a better way?

Thanks
Vincent Davis
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