[web2py] call function in template layout

[bussiere adrien]

i would like to know if it's possible to call a home made function in a 
template.
i've made this gist and i would like to call it in template :
https://gist.github.com/2032147 

like : {{ encadrement(form)  }}

And where to place my gist to call it in template.
And if not, where to put this functino to call it before template.

regards
Bussiere