Need for

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.4/plpython-subtransaction.html
Description:

The name "transaction" and all examples (update,etc.) are for
transactions... It is not evident for commom reader that we can use
`plpy.execute('select f()')` that is very important, the reuse of non-python
functions.

So. suggestion: say that there are a returning value from plpy, and showing
an example of simple function call,
like `y = plpy.execute('SELECT f()')`.