why is python slow?

[les ander]

Hi,
i am just curious as to why different programming languages have different
speed. I understand that if a language has an extensive grammar
(such as c++) the compiler would take longer. But what about execution?
why is a perl program faster than similar python program? For example
when java came out it use to be pretty slow, but now it is pretty fast. How
was this speed-up acheived and why is it not possible to have such a speed up
for python?

thanks 
les

P.S. I am just trying to understand and do not intend to put down python by 
any means.