Question

I have two instances of an object in a list

class Thing():
     timeTo = 0
     timeFrom = 0
     name = ""

o1 = Thing()
o1.name = "One"
o1.timeFrom = 2

o2 = Thing()
o2.timeTo = 20
o2.name = "Two"

myList = [o1, o2]


biggestIndex = (myList[0].timeFrom < myList[1].timeTo) & 1
bigger  = myList.pop(biggestIndex)
lesser  = myList.pop()

print bigger.name
print lesser.name

both o1 and o2 have two properties that I want to compare the first in the lists timeFrom property and the second ones timeTo property to eachother.

I feel this is a bit awkward and wierd, is there perhaps a better and more readable approach to this?

Answer 1

The best solution is to make Thing instances sortable. You do this by implementing __lt__:

class Thing():
     timeTo = 0
     timeFrom = 0
     name = ""

     def __lt__(self, other):
         return self.timeFrom < other.timeTo


lesser, bigger = sorted(myList)

Python2 has lesser, bigger = sorted(myList, cmp=lambda one,other: one.timeFrom < other.timeTo).

In Python3 cmp is gone, I guess to force people to do (or learn) OOP and write a adapter.

class SortAdaper(object):
    def __init__(self, obj ):
        self.obj = obj

class TimeLineSorter(SortAdaper):
    """ sorts in a timeline """
    def __lt__(self, other):
        return self.obj.timeFrom < other.obj.timeTo

class NameSorter(SortAdaper):
    """ sorts by name """
    def __lt__(self, other):
        return self.obj.name < other.obj.name

print sorted( myList, key=TimeLineSorter)
print sorted( myList, key=NameSorter)