## Saturday, 28 July 2007

### Google Solvers: Python vs. Perl, Java and C++

It happened a couple of months ago. My distinguished colleague Stefan Z., a dyed in the wool C/C++ developer, educated on Dijkstra, Knuth and Wirth, wanted to learn Python to extend his horizon. As he's already got the basic free Python books from the web, he proceeded to coding of a simple example. He chose the Google problem: find the solution(s) of the equation "wwwdot - google = dotcom"*, and coded the greedy (or is it the brute-force?) solution. He showed it too me, and true to the motto "Doing science for fun and profit ;-)" I guessed it would be interesting to compare this code for speed and for visual appeal to its Perl equivalent. And then to Java.

Python code looked like this:
`#!/usr/bin/pythonprint "Program Start."for W in range(10): for D in range(10):   for O in range(10):   for T in range(10):     print "looking for W=", W, "D=", D, "O=", O, "T=", T       for G in range(10):         for L in range(10):           for E in range(10):             for C in range(10):               for M in range(10):                 a = 100000*W+10000*W+1000*W+100*D+10*O+T                 b = 100000*G+10000*O+1000*O+100*G+10*L+E                 s = a - b                 r = 100000*D+10000*O+1000*T+100*C+10*O+M                 if s == r:                   print "FOUND the solution: a=", a, "b=", b, "s=", s, "r=", r                   print "      W=", W, "D=", D, "O=", O, "T=", T, "G=", G, \                         "L=", L, "E=", E, "C=", C, "M=", Mprint "Program End."`
short and to the point!

The Perl code like that:

`#!/usr/bin/perl -wprint "Program Start.\n";for \$W (1..10) { for \$D (1..10) {   for \$O (1..10) {     for \$T (1..10) {       print "\nlooking for W=", \$W, "D=", \$D, "O=", \$O, "T=", \$T;       for \$G (1..10) {         for \$L (1..10) {           for \$E (1..10) {             for \$C (1..10) {               for \$M (1..10) {                 \$a = 100000*\$W+10000*\$W+1000*\$W+100*\$D+10*\$O+\$T;                 \$b = 100000*\$G+10000*\$O+1000*\$O+100*\$G+10*\$L+\$E;                 \$s = \$a - \$b;                 \$r = 100000*\$D+10000*\$O+1000*\$T+100*\$C+10*\$O+\$M;                 if (\$s == \$r) {                   print "\nFOUND the solution: a=", \$a, "b=", \$b, "s=",                         \$s, "r=",\$r;                   print "\n      W=", W, "D=", D, "O=", O, "T=", T, "G=",  G,                         "L=", L, "E=", E, "C=", C, "M=", M;                 }               }             }           }         }       }     }   } }}print "\nProgram End."`
so it wasn't that unreadable: actually a little more readable than Python by its usage of direct range expressions and curly braces to denote scopes. On the other side the brace doesn't add any useful information in this special example but can't be omitted, so maybe Python isn't so bad after all?

In Java code I skipped unneccesary braces a thing which... would not be possible in Perl:

`public class GoogleSolver{  public static void main(String[] args)  {    System.out.println("Program Start.");    int a=0, b=0, s=0, r=0;    for (int W=1; W <11; W++)      for (int D=1; D <11; D++)        for (int O=1; O <11; O++)          for (int T=1; T <11; T++)          {            System.out.println("looking for W="+ W+ " D="+ D+ " O="+ O+ " T="+ T);            for (int G=1; G <11; G++)              for (int L=1; L <11; L++)                for (int E=1; E <11; E++)                  for (int C=1; C <11; C++)                    for (int M=1; M <11; M++)                    {                      a = 100000*W+10000*W+1000*W+100*D+10*O+T;                      b = 100000*G+10000*O+1000*O+100*G+10*L+E;                      s = a - b;                      r = 100000*D+10000*O+1000*T+100*C+10*O+M;                      if (s == r)                      {                        System.out.println("FOUND the solution: a="+ a+ "b="+                                           b+ "s="+ s+ "r="+ r);                        System.out.println("      W="+ W+ "D="+ D+ "O="+ O+ "T="+                                           T+ "G="+ G+ "L="+ L+ "E="+ E+ "C="+                                           C+ "M="+ M);                      }                    }    System.out.println("Program End.");  }} `
so ist wasn't overly verbose except for System.out.println and the "public static main void" beast. Now the measurements on my Pentium IV (ca 3 GHz) with Redhat Enterprise Linux 3:

Perl: Program End. 2526.790u 0.310s 42:11.34 99.8% 0+0k 0+0io 244pf+0w
Python: Program End. 4494.230u 0.330s 1:15:00.51 99.8% 0+0k 0+0io 337pf+0w
Java: Program End. 38.847u 0.150s 0:38.86 100.3% 0+0k 0+0io 1pf+0w

Pretty interesting stuff here: Perl outperformed Python twice and Java was lightning fast! It seems Python's VM implementation isn't very sophisticated. OK, these are no scientifical experiments, but the numbers are reproducible and telling: Perl is pretty fast, and usable for some number crunching, Python is painlessly slow :-(, and Java is just good! Both Python and Perl are installed in a standard way in the /usr/bin directory, so there's no unfair network overhead involved! And Java deserves praise, considering that I used the most inefficient way of constructing the output strings!

Ok, I thought, now let's try something really fast, and I quickly recoded the algorithm in C++. Here I skipped unneccesary braces as well:
`#include <iostream>using namespace std;int main(){  cout << "Program Start.\n";  int a=0, b=0, s=0, r=0;  for (int W=1; W <11; W++)    for (int D=1; D <11; D++)      for (int O=1; O <11; O++)        for (int T=1; T <11; T++)        {          cout << "\nlooking for W="<< W<< "D="<< D<< "O="<< O<< "T="<< T;          for (int G=1; G <11; G++)            for (int L=1; L <11; L++)              for (int E=1; E <11; E++)                for (int C=1; C <11; C++)                  for (int M=1; M <11; M++)                  {                    a = 100000*W+10000*W+1000*W+100*D+10*O+T;                    b = 100000*G+10000*O+1000*O+100*G+10*L+E;                    s = a - b;                    r = 100000*D+10000*O+1000*T+100*C+10*O+M;                    if (s == r)                    {                      cout << "\nFOUND the solution: a="<< a<< "b="<< b<< "s="                           << s<< "r="<< r;                      cout << "\n      W="<< W<< "D="<< D<< "O="<< O<< "T="                           << T<< "G="<< G << "L="<< L<< "E="<< E<< "C="                           << C << "M="<< M;                    }                  }                }  cout << "\nProgram End.";}`
The code is little less verbose than of Java example, but will it run better? For all we know it should! Then I run my measurements and got a little shock:

C++: Program End. 37.420u 0.060s 0:37.92 98.8% 0+0k 0+0io 197pf+0w
Java: Program End. 38.847u 0.150s 0:38.86 100.3% 0+0k 0+0io 1pf+0w

So C++ was better, but by a very small margin!** You can see the JIT technologiy is working very good for this example: the JIT compiler must run only unfrequently and then the machine code is invoked all the time! Ok, so maybe this marketing drivel about Java speed being the same as C++ isn't all that wrong? Admittedly, C++ streams aren't the latest cry in performance, but I wanted to write standard code, without tweaks for optimization...

But wait, I thought. I remember some article on whole program optimization, and it said that Java people think C++ cannot optimize and that only JVM can. Think, think... Did you used the -O switch??? Of course I didn't, so the measurement is pretty unfair on C++ here. I repeated the measurement with gcc's -O2 optimization:

C++: Program End. 8.030u 0.010s 0:08.41 95.6% 0+0k 0+0io 199pf+0w

OK, that was reeeaaaaally fast, indeed.

So recapitulating: Perl was 2 times faster than Python, Java 2 orders of magnitude faster than both of them and C++ 1 order of magnitude faster than Java. So no surprises here. Except for Python's bad performance. So programming in the dynamically typed languages isn't always so much fun!*** In C++ you know when you are using language construct, that tey'll be rather fast, and when you are using STL you'll have your big-Oh complexity documented. But when you're using Python you don't know anything! Or you must google for implementation details of lists, tuples etc, and do some code tweaking. By the way, does anyone know why Perl is faster than Python? Does its VM do some instruction cashing that Python's doesn't? Would Jython be faster, as it can enjoy benefits of the massively optimized JVM? Maybe I should try it out...

----
* This is typically Google. They adversized one time with this line: "www.{first 10-digit prime found in consecutive digits of e}.com" or similar. The idea was to to find the people who can solve the problem inside of {}, i.e. use the prime distribution theorem, and hire them.

** On another machine it was even a little slower:
C++: Program End.44.552u 0.077s 0:44.64 99.9% 0+0k 0+0io 0pf+0w

*** see for example Uncle Bob's:http://www.artima.com/weblogs/viewpost.jsp?thread=4639 