Python Exceptions: EAFP and What is Really Exceptional?

Question

It\'s been said in a couple places (here and here) that Python\'s emphasis on \"it\'s easier to ask for forgiveness than permission\" (EAFP) should be tempered with the idea

Answer 1

Looking at the docs I think you can safely re-write the function as follows:

import heapq
...
pq = heapq.heapify(a_list)
while pq:
    min1 = heapq.heappop(pq)
    if pq:
        min2 = heapq.heappop(pq)
        heapq.heappush(pq, min1 + min2)
# do something with min1

..and thereby avoid the try-except.

Getting to the end of a list which is something you know is going to happen here isn't exceptional - it's garaunteed! So better practice would be to handle it in advance. If you had something else in another thread which was consuming from the same heap then using try-except there would make a lot more sense (i.e. handling a special / unpredictable case).

More generally, I would avoid try-excepts wherever I can test for and avoid a failure in advance. This forces you to say "I know this bad situation might happen so here's how I deal with it". In my opinion, you'll tend to write more readable code as a result.

[Edit] Updated the example as per Alex's suggestion