Agree that while raw speed is important, in most situations it wouldn't be the most important reason to choose one programming language over another.
I came from the angle of an engineer in a small company. For myself, the main attraction of Julia was the easiness to achieve decent speed without making much explicit effort: that means what feels more natural vectorized will be vectorized, while what feels more natural in a loop will be in a loop; that means I don't need to resort to another language or a library only for improving speed; and that means apart from sticking to a couple good habits, I can use objects, functions etc. the same way inside a loop vs. outside. None of these is critical by itself, but they add up to an uninterrupted flow of thoughts while writing code to explore, try, fail, and retry, for many iterations. During this "less careful" prototyping, 1-2x slow down is fine, but with Julia I know I won't sit there for tens of minutes waiting for a result while debating myself whether I should rewrite it in C++ or rehaul the code with Cython etc.; instead I can rest assured that as long as my algo and coding have no mistakes or major flaws, the speed is close to what I will get even if I make several times more effort to rewrite it in C++. Another big deal for me is the resulted removal of the barrier between prototype and production code. For production I can review and improve my code carefully, but rewriting it in a less expressive language is too much. I was a huge fan of Python (heck I even persuaded my previous boss, a VP, to pick up Python - though I don't know if he really had time to finish it. :-)). However, the slow raw speed and the over-freedom to change class definition anywhere always gave me the itch to find something better. My brother at JPL who worked on Python projects also complained about having to think really hard to vectorize almost everything and then couldn't easily understand what he was doing a few months later because the code was too unnatural for the problem; the indentation was also a big headache as collaborators use different editors with different tab definitions. So I'm really happy to have found Julia, which gave me the same joy as coding in Python and removed the main itches. -Zhong
