computing a weighted sum

[Will McGugan]

andreif at mail.dntis.ro wrote:
> Suppose I have a list of n floats x and a list of n floats w and I want
> to compute x[0]*w[0] + .. + x[n-1]*w[n-1].
> 
> Is there some elegant expression (perhaps using lambda) to have it done
> in one statement ? As in :
>      y = lambda x,w : ...
> 
> I ask because the way I am doing it now :
>       y = 0
>       for i in range(0,n): y += x[i]*w[i]
> 
> doesn't seem very pythonic :)
> 
I'll take a stab at that!

In Python 2.3

sum( [ _x * _w for _x, _w in zip( x, w ) ] )

or in 2.4

sum( _x * _w for _x, _w in zip( x, w ) )

You may want to use itertools.izip in place of zip if the lists are large.

Will McGugan