Lighttpd + webpy + venv: how to configure

Question

I'm trying to run webpy as fastCgi inside lighttpd in my Debian system. Webpy asked for Flup and cheroot in order to work, so I created a virtual environment and I managed to have it running inside the venv (where I installed Flup and cheroot using pip), using those commands:

source .venv/bin/activate
python code.py

This way it runs (the file code.py contains the source code showed in the webpy tutorial). I was forced to install the packages using pip and venv because if I try to install python packages from apt I receive the PEP668 EXTERNALLY-MANAGED error.

What I'm trying to do is to have it run served by lighttpd. I modified the /etc/lighttpd/conf-available/10-fastcgi.conf as follows:

# /usr/share/doc/lighttpd/fastcgi.txt.gz
# http://redmine.lighttpd.net/projects/lighttpd/wiki/Docs:ConfigurationOptions#mod_fastcgi-fastcgi

server.modules += ( "mod_fastcgi" )
server.modules += ( "mod_rewrite" )
 fastcgi.server = ( "/code.py" =>
 (( "socket" => "/tmp/fastcgi.socket",
    "bin-path" => "/var/www/ltm/.venv/bin/python3 /var/www/ltm/code.py",
    "max-procs" => 1,
    "bin-environment" => (
        "REAL_SCRIPT_NAME" => ""
   ),
   "check-local" => "disable"
 ))
 )


 url.rewrite-once = (
   "^/favicon.ico$" => "/static/favicon.ico",
   "^/static/(.*)$" => "/static/$1",
   "^/(.*)$" => "/code.py/$1",
 )

This way it seems to work but, when I move on on the tutorial and start using templates it stops working (I receive the error: No template named index). I'm quite sure that the bin-path setting is wrong, but that's the only way I could make it run.

What's the correct way of handling this configuration?