16085
Question:
I have heard good stuff about PyPy. In particular I'd heard that it was very fast which made me wonder if it might be usable for an embedded project I have.
I downloaded PyPy-2.6 for my Windows 7 PC, and unzipped the contents into a directory.
I've written a small test program to allow me to benchmark:
import time
def fib(n):
if n == 0 or n == 1:
return 1
return fib(n - 1) + fib(n - 2)
t0 = time.time()
fib(20)
t1 = time.time()
print t1-t0
So I went to the directory where PyPy was unzipped, ran ./pypy.exe hello.py and got an answer of 0.120.
Then I fired up a cygwin console and ran python hello.py and got an answer of 0.01.
Am I using PyPy wrong or is it only faster for certain applications?
<strong>Edit</strong>
Thanks to Rob who pointed out that the JIT compiler needs time to warm up.
Extending my sample code produces the following results:
n PyPy Python 20 0.12 0.01 25 0.15 0.06 30 0.34 0.67 35 0.92 7.39 40 10.98 82.9It seems like there's a 0.1 second start-up cost or something, but after that it's faster.
Answer1:It is only faster for certain applications. Quoting the <a href="http://pypy.org/features.html" rel="nofollow">PyPy doc</a>:
<blockquote>There are two cases that you should be aware where PyPy will not be able to speed up your code:
<ul><li>Short-running processes: if it doesn't run for at least a few seconds, then the JIT compiler won't have enough time to warm up.
</li> <li>If all the time is spent in run-time libraries (i.e. in C functions), and not actually running Python code, the JIT compiler will not help.
</li> </ul></blockquote>Since your program seems to run on the order of 10<sup><sup>-</sup>2</sup> or 10<sup><sup>-</sup>1</sup> seconds, the JIT compiler doesn't do you any good.
