> The problem was I wrote the parser in C. This is what enabled good performance. When my manager came back to work, she realized she declared that she doesn't know C and will never learn (even though she wasn't related directly to the project), and the project was thrown to the dogs.

I sympathize with your manager here. If someone under me, ostensibly working on a Python app, wrote a component in C while I was away on leave, without clearing it with me first, I'd be pissed off too.

You decided to use a programming language that other people on your team didn't know, and therefore nobody other than you could maintain, debug, or extend what your wrote. And you did it underhandedly while your manager was away. You deserved the ire here.

There are lots of other ways you can make things closer to C-level performance while sticking closer to something a team of Python devs could maintain, e.g. using Cython or even running a Python program with PyPy (especially if it involves a lot of looping and basic string operations).

And did you even benchmark the Python implementation? How much faster was the C version really? Was it even a bottleneck in the system to begin with? How many developer-hours did you spend on the C version of this component, and how many would you have spent on the equivalent Python version?

Also, C is a really hard language to learn and use effectively, because of the loosey-goosey types and absence of memory safety. Your decision imposed a tremendous burden on the rest of the organization, which might not have been worth the performance gain in this one component of your system.

This was IMO a bad decision on your part, because it's overly fixated on the benefits of achieving a narrow technical objective, disregarding a variety of short- and long-term costs. At minimum, it's not at all obvious that your decision aligns with the broader goal of your team consistently delivering value over a longer period of time. There are countless war stories to be told, of overzealous junior- and mid-level ICs pulling shit like this and it ending up badly for the org.

It's one thing if another team actually committed to using a different programming language, and then backed off their commitment, as in the Haxe example. That's on them, not on you. But being a cowboy and writing stuff in hard-to-learn languages that other people on your team don't know, without any org-level buy-in for getting people trained up on it, is not at all a good habit to be in. Consider that you are the only common factor among all these problematic situations at different organizations.