Asked By – Jonathan Livni
What would be the most elegant and efficient way of finding/returning the first list item that matches a certain criterion?
For example, if I have a list of objects and I would like to get the first object of those with attribute
obj.val==5. I could of course use list comprehension, but that would incur O(n) and if n is large, it’s wasteful. I could also use a loop with
break once the criterion was met, but I thought there could be a more pythonic/elegant solution.
Now we will see solution for issue: Find first sequence item that matches a criterion [duplicate]
If you don’t have any other indexes or sorted information for your objects, then you will have to iterate until such an object is found:
next(obj for obj in objs if obj.val == 5)
This is however faster than a complete list comprehension. Compare these two:
[i for i in xrange(100000) if i == 1000] next(i for i in xrange(100000) if i == 1000)
The first one needs 5.75ms, the second one 58.3µs (100 times faster because the loop 100 times shorter).