PostgreSQL: how to install plpythonu extension

You're using a PostgreSQL package from Bitnami, in /opt. It's not clear if you installed this with apt-get or via an installer script/program, but in either case it's not the same PostgreSQL as what's in the Ubuntu postgresql package.

Installing postgresql-plpython won't do you any good, because you're installing PL/Python support for a different PostgreSQL install than the one you're actually using.

You'll need to use the same installation method you originally used to install the Bitnami PostgreSQL to add PL/Python support, if it's available. It might not be provided by Bitnami.

Otherwise, if you're not too attached to using Bitnami's PostgreSQL, you could use the recommended packages from http://apt.postgresql.org/ .

for postgres 11.2 (Debian based) I needed to install:

apt-get update && apt-get install postgresql-plpython3-11