Programming Forums > Application Development > Java

Arevos · Aug 21st, 2005, 5:05 AM

Quote:

Originally Posted by OpenLoop

Didn't know that Python compiles, but it still slow compared to Java and too slow compared to C++. See my thread where i made a small comparison
Thanks for the info and the GCJ link.

Using xrange instead of range speeds up the python implementation by about 40%, but yep, Python is certainly not the language to use for low level stuff! That said, Python gets around this by making it relatively simple to write modules in C or C++, so in theory, any low level, CPU-intensive code can be farmed out to C. However, this has the disadvantage of tying Python to one platform.

This benchmarking stuff looks rather interesting, so I benchmarked a few languages myself with the primes algorithm:

(Toggle Plain Text)

# GCC: primes.c
int main() {
  int n = 0, d = 0;
  for (n = 2; n < 50000; n++) {
    for (d = 2; d < n/2 + 1; d++) {
      if (n % d == 0) {
        break;
      }
    }
  }
}
# Time to run: 971 milliseconds

# Java 1.5.0
public class primes {
  public static void main(String[] args) {
    int n = 0, d = 0;
    for (n = 2; n < 50000; n++) {
      for (d = 2; d < n/2 + 1; d++) {
        if (n % d == 0) {
          break;
        }
      } 
    }
  }
}
# Time to run: 1098 milliseconds

# Python 2.4.1 (using range)
for n in range(2,50000):
    for d in range(2,n/2+1):
        if (n % d == 0):
            break
# Time to run: 33346 milliseconds

# Python 2.4.1 (using xrange)
for n in xrange(2,50000):
    for d in xrange(2,n/2+1):
        if (n % d == 0):
            break
# Time to run: 19900 milliseconds

# Perl 5.8.4
for ($n = 2; $n < 50000; $n++) {
	for ($d = 2; $d < $n / 2 + 1; $d++) {
		if ($n % $d == 0) {
			last;
		}
	}
}
# Time to run: 31798 milliseconds

# Nice 0.11.0 (using legacy for loops)
void main(String[] args) {
  for (int n = 2; n < 50000; n++) {
    for (int d = 2; d < n/2 + 1; d++) {
      if (n % d == 0) {
        break;
      }
    }
  }
}
# Time to run: 1041 milliseconds

# Nice 0.11.0 (using new for loops)
void main(String[] args) {
  for (int n : 2..50000)
    for (int d : 2..(n/2 + 1))
      if (n % d == 0)
        break;
}
# Time to run: 3752 milliseconds

# Ruby 1.8.2
for n in 2..50000
  for d in 2..(n/2 + 1)
    break if (n % d == 0)
  end
end
# Time to run: 92141 milliseconds

OpenLoop · Aug 21st, 2005, 9:29 AM

Wow this xrange is powerful stuff. How come it was not mentionned in the Python tutorial. (or maybe i didn't get that far in the tutorial)
You should start a thread in the Python forums "range vs xrange" and let the Pythoners know the difference.

Arevos · Aug 21st, 2005, 10:02 AM

As I understand it, range returns a sequencial list of integers, whilst xrange returns an object that pretends to be a sequencial list of integers. So using 'range(50000)' in a for loop requires Python to create a list of 50'000 integers, whilst the xrange object just returns the integer needed.

If you want to think about it in Java terms, xrange might look something like:

(Toggle Plain Text)

class XRange implements List {
  private int n;
  XRange(int n) {
    this.n = n;
  }

  ...

  Iterator iterator() {
    return new Iterator(n) {
      private int i = 0;
      private int n = 0;
      Iterator(int n) {
        this.n = n;
      }
      boolean hasNext() {
        return i < n;
      }
      Object next() {
        i += 1
        return Integer(i - 1);
      }
      void remove() {}
    }
  }

  ...

}

Aug 21st, 2005, 10:02 AM	#13
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	As I understand it, range returns a sequencial list of integers, whilst xrange returns an object that pretends to be a sequencial list of integers. So using 'range(50000)' in a for loop requires Python to create a list of 50'000 integers, whilst the xrange object just returns the integer needed. If you want to think about it in Java terms, xrange might look something like: (Toggle Plain Text) class XRange implements List { private int n; XRange(int n) { this.n = n; } ... Iterator iterator() { return new Iterator(n) { private int i = 0; private int n = 0; Iterator(int n) { this.n = n; } boolean hasNext() { return i < n; } Object next() { i += 1 return Integer(i - 1); } void remove() {} } } ... } class XRange implements List { private int n; XRange(int n) { this.n = n; } ... Iterator iterator() { return new Iterator(n) { private int i = 0; private int n = 0; Iterator(int n) { this.n = n; } boolean hasNext() { return i < n; } Object next() { i += 1 return Integer(i - 1); } void remove() {} } } ... }

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Aug 21st, 2005, 9:29 AM	#12
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	Wow this xrange is powerful stuff. How come it was not mentionned in the Python tutorial. (or maybe i didn't get that far in the tutorial) You should start a thread in the Python forums "range vs xrange" and let the Pythoners know the difference.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Programming Forums > Application Development > Java

Java vs Python and C++