Python interpreter speed

[Tim Wintle]

On Sun, 2009-04-19 at 18:11 +0200, Ryniek90 wrote:
> Hi.
> 
> Standard Python interpreter's implementation is written in C language. C 
> code while compilation, is compilled into machine code (the fastest 
> code). Python code is compiled into into byte-code which is also some 
> sort of fast machine code. So why Python interpreter is slower than Java 
> VM? Being written in C and compilled into machine code, it should be as 
> fast as C/Asm code.
> What's wrong with that?


I can't remember Java properly, but...

Firstly, speed will depend on what you're writing. I dont' actually know
how much slower python is, but I'm sure there are some things that run
faster in python.

for example, the program:

#!/usr/bin/python
print "Hello World"

is almost certainly faster in python than Java, as the JVM takes much
longer to start up.


But basically for the actual code execution speed, it's the Virtual
machine:

Dynamic typing ...
is great for productivity, and a great language feature, but it does
mean that most operations in the virtual machine have to be wrapped in
some kind of type-checking. That adds more and more operations to the
work that has to be done to run python code.

Just in Time ...
is used in the Java VM but not in the standard python VM. It can
significantly optimise performance though.

There are various people working on adding a JIT to python - I'm most
interested in pypy, here's a basic article explaining their current
target of adding a tracing JIT ( I believe it's working on a small
subset of python):
http://morepypy.blogspot.com/2009/03/applying-tracing-jit-to-interpreter.html


(Just spotted that there was a new pypy release yesterday if people
haven't noticed)


You'll also probably notice that many of python's types (list, dict,
etc.) might be slower for small sizes than Java's are - that's because
they have been optimised to perform efficiently at any size, at the
expense of being slightly less efficient than they could be for small
sizes)


Tim Wintle