Profiling is super cool, but we need to know when it is appropriate to do it, and in what measure we need to address the results we get from it.

Donald Knuth once said, "premature optimization is the root of all evil", and, although I wouldn't have put it down so drastically, I do agree with him. After all, who am I to disagree with the man who gave us The Art of Computer Programming, TeX, and some of the coolest algorithms I have ever studied when I was a university student?

So, first and foremost: correctness. You want your code to deliver the correct results, therefore write tests, find edge cases, and stress your code in every way you think makes sense. Don't be protective, don't put things in the back of your brain for later because you think they're not likely to happen. Be thorough.

Second, take care of coding best practices. Remember the following—readability, extensibility, loose coupling, modularity, and design. Apply OOP principles: encapsulation, abstraction, single responsibility, open/closed, and so on. Read up on these concepts. They will open horizons for you, and they will expand the way you think about code.

Third, refactor like a beast! The Boy Scouts rule says:

Apply this rule to your code.

And, finally, when all of this has been taken care of, then and only then, take care of optimizing and profiling.

Run your profiler and identify bottlenecks. When you have an idea of the bottlenecks you need to address, start with the worst one first. Sometimes, fixing a bottleneck causes a ripple effect that will expand and change the way the rest of the code works. Sometimes this is only a little, sometimes a bit more, according to how your code was designed and implemented. Therefore, start with the biggest issue first.

One of the reasons Python is so popular is that it is possible to implement it in many different ways. So, if you find yourself having trouble boosting up some part of your code using sheer Python, nothing prevents you from rolling up your sleeves, buying 200 liters of coffee, and rewriting the slow piece of code in C—guaranteed to be fun!