This problem bugged me because it's a trivial sort and yet the outcomes were markedly different in Python 3.6, depending on how you approach it.

Some speculate that sort() is faster than sorted(), but these functions are basically the same except the former is an in-place sort (which shouldn't matter here).

Edit: sorted() is a wrapper for sort(). See also: https://stackoverflow.com/questions/1915376/is-pythons-sorted-function-guaranteed-to-be-stable

Analysis with cprofile kept reporting that print() was the cause of the slowdown, which made no sense at first.

It turned out that int -> str conversions (whether by print or explicitly converting the values first) are surprisingly costly (probably far more costly with huge integers, as test cases #4, #5, and #6 appear to contain). If you're taking the "convert to int, sort, then print" route, you're actually printing ints, which are converted internally to strings for display. And that's why print becomes slow.

First, a typical slow implementation (I originally had a longer form for these - the list comprehension here makes it more compact but not noticeably faster):

for i in sorted([int(s) for s in unsorted]):
    print(i) # int to str = costly

Adding an int -> str conversion before print doesn't help - in fact, it gets a little bit slower:

for i in sorted([int(s) for s in unsorted]):
    s = str(i) # This is a costly step
    print(s)

However, using the key=int sorting argument performs the necessary conversions internally during the sort process itself, while returning the original string values that are quickly printed. (Note that the argument to key is the name of a function that takes one argument, in this case int().) I'm going to guess that str -> int is much faster than int -> str

A fast (challenge-friendly) in-place sort():

unsorted.sort(key=int)
for s in unsorted:
    print(s)

sorted() is virtually the same speed, and doesn't modify unsorted:

for s in sorted(unsorted, key=int):
    print(s)

For grins, let's make it slow again (in fact, this becomes slowest of all the attempts!):

for s in sorted(unsorted, key=int):
    i = int(s) # Forces costly int -> str conversion in print()
    print(i)

More info:

• https://docs.python.org/3.6/library/functions.html?highlight=sorted#sorted
• https://docs.python.org/3.6/library/profile.html#profile.Profile