stateful embedded postgres python functions

stateful-embedded-postgres-python-functions.sh

#
# description: demo of shared data in plpython functions
# by: Cody Kochmann
# date: 2021-10-02
#
testdb=> -- pg has two magic vars for plpython3u functions
testdb=> -- SD | dict | per function memory
testsb=> -- GD | dict | global shared function memory
testdb=> CREATE FUNCTION state_test (t TEXT)
  RETURNS TEXT[]
AS $$
  SD["data"] = SD["data"] + [t] if "data" in SD else [t]
  return SD["data"]
$$ LANGUAGE plpython3u;
CREATE FUNCTION
testdb=> SELECT state_test('waffles');
 state_test 
------------
 {waffles}
(1 row)

testdb=> SELECT state_test('are');
  state_test   
---------------
 {waffles,are}
(1 row)

testdb=> SELECT state_test('better');
      state_test      
----------------------
 {waffles,are,better}
(1 row)

testdb=> SELECT state_test('than');
        state_test         
---------------------------
 {waffles,are,better,than}
(1 row)

testdb=> SELECT state_test('pancakes');
             state_test             
------------------------------------
 {waffles,are,better,than,pancakes}
(1 row)