I think if you can, by editing the title in the original, coalesce two questions into one, then deleting is still ok. Not every duplicate needs to be kept and with some manipulation you can make the original easier to find and remove the need for the duplicate. I don't know that the referenced question is a particularly good example of that, though changing the title of the first to:
How can I do a line break or continuation of code in Python?
might suffice to make the second question unneeded. The reason I say that, is that the question is relatively simple and the answers nearly identical in content.
In some cases, however, the question might not be worth keeping, but the answers in the duplicate may be. In that case, merging questions might be a better option and I would flag for moderator attention if that were the case.
Note, too, that there is a risk with duplicates -- the search may find the question with an answer that is not as good as the original, in fact, there's no guarantee that it won't be wrong. A question closed as a duplicate may not get the attention it needs to have a correct answer emerge as the best. Merging questions, where feasible, could avoid this.