visualpython-users

[Visualpython-users] Speed?!

[Susanne M. <sus...@un...>]

Hi,

I was very amazed yesterday when I wanted to calculate a simple thing
with Python. I typed

for a in range(200):
    for b in range(200):
        for c in range(200):
            pass

and it took over 10 seconds! I typed the same thing in Borland Delphi
(on the same machine, a Pentium III) and it was immediate. One wouldn't
even realize that it was calculating. In C++ it was slightly slower than
in Delphi, but by far not as slow as Python. Why is it so terribly slow,
even if it doesn't need to calculate anything? Is there a possibility
for accelerating this? 

thanks
Susanne

-- 
-------------------------------------------------------
Susanne Moelbert
Universite de Fribourg
Departement of Theoretical Physics
CH-1700 Fribourg	
Switzerland		
			

Phone: ++41 (0)26 300 91 46  (office)
       ++41 (0)26 424 19 33  (home)
e-mail: sus...@un...

my homepage: http://ptheosg00.unifr.ch/~moelbert/
-------------------------------------------------------

Re: [Visualpython-users] Speed?!

[Markus G. <gr...@iu...>]

Susanne Moelbert wrote:

> Hi,
>
> I was very amazed yesterday when I wanted to calculate a simple thing
> with Python. I typed
>
> for a in range(200):
>     for b in range(200):
>         for c in range(200):
>             pass
>
> and it took over 10 seconds! I typed the same thing in Borland Delphi
> (on the same machine, a Pentium III) and it was immediate. One wouldn't
> even realize that it was calculating. In C++ it was slightly slower than
> in Delphi, but by far not as slow as Python. Why is it so terribly slow,
> even if it doesn't need to calculate anything? Is there a possibility
> for accelerating this?

Well, I guess the situation is this:

Delphi trys to optimize the code at compile time.  It recognizes, that
there is really nothing to do, so the whole loop construct is optimized
away.

C++ would probably be as fast as Delphi if you compile with -O3 or
something like this.

Python does no optimizations, so Python is really performing the loops,
even if there is nothing to do.  So in a real world example there would of
course be something to do in the inner loop, so Delphi and C++ won't return
emmediate.  The other point is that Python is interpreted (even if the
script is translated to bytecode before), and scripting languages tend to
be 20 to 30 times slower than compiled ones.  But if you want short
turn-around times, and want to have fun during programming, ...

Markus

Re: [Visualpython-users] Speed?!

[Ari H. <ahe...@an...>]

On Mon, Apr 23, 2001 at 12:59:15PM +0200, Markus Gritsch wrote:
> Delphi trys to optimize the code at compile time.  It recognizes, that
> there is really nothing to do, so the whole loop construct is optimized
> away.
> 
> C++ would probably be as fast as Delphi if you compile with -O3 or
> something like this.

Both quite true. But there does remain an issue of speed when there *is*
actual computation in the loop.

> 
> Python does no optimizations, so Python is really performing the loops,
> even if there is nothing to do.  So in a real world example there would of
> course be something to do in the inner loop, so Delphi and C++ won't return
> emmediate.  The other point is that Python is interpreted (even if the
> script is translated to bytecode before), and scripting languages tend to
> be 20 to 30 times slower than compiled ones.  But if you want short
> turn-around times, and want to have fun during programming, ...
> 
Python is a *very* slow language.

The way to do this efficiently is with the Numeric package, which allows you
to treat multidimensional arrays as primitive datatypes. In general,
operations using Numeric can be within a factor of 2 or 3 of C (that is darn
fast, especially considering that Python is one of the slowest languages
around).

There is an excellent Numeric tutorial at
  http://starship.python.net/~da/numtut/array.html



ari

Re: [Visualpython-users] Speed?!

[Anton S. <br...@po...>]

Susanne Moelbert wrote:
> I was very amazed yesterday when I wanted to calculate
> a simple thing with Python. I typed
> 
> for a in range(200):
>     for b in range(200):
>         for c in range(200):
>             pass
> 
> and it took over 10 seconds! . . .

range() works by creating a list [0, 1, ... 199].
The above code appears to do that 40201 times.

This saves about half the time:

	spam = range(200)
	for a in spam:
	  for b in spam:
	    for c in spam:
	      pass

-- 
Anton Sherwood  --  br...@p0...  --  http://ogre.nu/