PL/Python allows you to write functions in the Python programming
language that may be used in SQL queries as if they were built into
Postgres.  The PL/Python intepreter is a full Python interpreter.

PL/Python is currently only available as an "untrusted" language
(meaning it does not offer any way of restricting what users can do
in it).  It has therefore been named "plpythonu".  The trusted variant
plpython may become available again in future, if a new secure execution
mechanism is developed in Python.