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12.3.2 Null, None

If an SQL null value is passed to a function, the argument value will appear as None in Python. The above function definition will return the wrong answer for null inputs. We could add STRICT to the function definition to make PostgreSQL do something more reasonable: if a null value is passed, the function will not be called at all, but will just return a null result automatically. Alternatively, we could check for null inputs in the function body:

CREATE FUNCTION pymax (a integer, b integer)
  RETURNS integer
AS $$
  if (a is None) or (b is None):
    return None
  if a > b:
    return a
  return b
$$ LANGUAGE plpythonu;

As shown above, to return an SQL null value from a PL/Python function, return the value None. This can be done whether the function is strict or not.