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12.3.3 Arrays, Lists

SQL array values are passed into PL/Python as a Python list. To return an SQL array value out of a PL/Python function, return a Python sequence, for example a list or tuple:

CREATE FUNCTION return_arr()
  RETURNS int[]
AS $$
return (1, 2, 3, 4, 5)
$$ LANGUAGE plpythonu;

SELECT return_arr();
 return_arr
-------------
 {1,2,3,4,5}
(1 row)

Note that in Python, strings are sequences, which can have undesirable effects that might be familiar to Python programmers:

CREATE FUNCTION return_str_arr()
  RETURNS varchar[]
AS $$
return "hello"
$$ LANGUAGE plpythonu;

SELECT return_str_arr();
 return_str_arr
----------------
 {h,e,l,l,o}
(1 row)