Friday, July 25

Things that will not change in Python 3000

A useful PEP for you to read:

Thursday, July 17

Why is C faster than Python?

Questioning the obvious is something we do a lot accidently (and get chided for it), but occasionally it yields some useful insights. A while back, there was a discussion on the pygame mailing list about languages and speed. The poster was insistent that there was no good reason why C was faster than Python. Below is my explanation, which in writing I realized I had never voiced this way before:

When there is no better algorithm, then using a higher performing language is about the only option you have for better performance. There is an even better option, dedicated hardware, but that is far beyond the reach of most mere mortals. But that's the reason why we have things like SIMD instruction sets, GPUs and physics co-processors.

All this conjecturing about Python performance in relation to compiled languages makes me wonder. Why is the performance of C code not as good as that of well-written hand-coded assembler? Surely if the machine can do it, C can?

The problem boils down to one of specificity. Any language that tells the computer more specifically what to do can be faster than one that doesn't. Unfortunately, telling the computer what to do specifically is not a productive way to solve most problems. I'd rather not have to tell the computer which machine codes to execute, but if I did, and I was clever, I could make my program the fastest possible -- for a given specific architecture at least.

Python is more abstract and general than C, C is more abstract and general than machine code. Therefore machine code is potentially faster than C, and C is potentially faster than Python. And unless you reduce the generality of Python, it will always be possible to write faster programs in C, given a competent compiler.

JITs (e.g., psyco) can help mitigating this, but they too are ultimately constrained by Python's expressive power.

So unless you are proposing to reduce Python's expressive power, you are waging a losing battle. Until which time machine intelligence exceeds our own, it will always be possible for a human programmer to get higher performance from the lower-level language. And I further propose that when the time arrives that machine intelligence exceeds our own, this will not be the problem foremost on my mind ;^)