why python is slower than java?

[Alex Martelli]

On 2004 Nov 06, at 08:31, Maurice LING wrote:
    ...
> 1. it is a disk intensive I/O operation.
> 2. users delay is not in the equation (there is no user input)
> 3. I am not interested in the amount of time needed to develop it. But 
> only interested execution speed.

OK, could you provide a simple toy example that meets these conditions 
-- does lot of identical disk-intensive I/O "in batch" -- and the 
execution speed measured (and on what platform) for what Python and 
Java implementations, please?

For example, taking a trivial Copy.java from somewhere on the net:

import java.io.*;

public class Copy {
     public static void main(String[] args) throws IOException {
         File inputFile = new File("/usr/share/dict/web2");
         File outputFile = new File("/tmp/acopy");

         FileReader in = new FileReader(inputFile);
         FileWriter out = new FileWriter(outputFile);
         int c;

         while ((c = in.read()) != -1)
            out.write(c);

         in.close();
         out.close();
     }
}

and I observe (on an iBook 800, MacOSX 10.3.5):

kallisti:~ alex$ java -version
java version "1.4.2_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_05-141.3)
Java HotSpot(TM) Client VM (build 1.4.2-38, mixed mode)

-r--r--r--  1 root  wheel  2486825 12 Sep  2003 /usr/share/dict/web2

kallisti:~ alex$ time java Copy

real    0m7.058s
user    0m5.820s
sys     0m0.390s

versus:

kallisti:~ alex$ time python2.4 Copy.py

real    0m0.296s
user    0m0.080s
sys     0m0.170s

with Python 2.4 beta 1 for the roughly equivalent:

inputFile = file("/usr/share/dict/web2", 'r')
outputFile = file("/tmp/acopy", 'w')

outputFile.write(inputFile.read())

inputFile.close()
outputFile.close()

which isn't all that far from highly optimized system commands:

kallisti:~ alex$ time cp /usr/share/dict/web2 /tmp/acopy

real    0m0.167s
user    0m0.000s
sys     0m0.040s

kallisti:~ alex$ time cat /usr/share/dict/web2 >/tmp/acopy

real    0m0.149s
user    0m0.000s
sys     0m0.090s


I'm sure the Java version can be optimized easily, too -- I just 
grabbed the first thing I saw off the net.  But surely this example 
doesn't point to any big performance issue with Python disk I/O wrt 
Java.  So, unless you post concrete examples yourself, the smallest the 
better, it's going to be pretty difficult to understand where your 
doubts are coming from!


Alex