[Orgmode] Exporting after executing code

[andrea Crotti]

Maybe it's a simple answer, but I haven't seen it in the manual.

Is there a possibility to insert code like

#+BEGIN_SRC python
print hello
#+END_SRC

which when exported gets substituted to what returned by the result 
of the code execution??

I think that I maybe need to customize the function in publishing 
variables, is that right?

And another thing, is there an easy way to include a file like
\include or \input in latex??
THanks all