Change schema of multiple PostgreSQL functions in one operation?

Recently I needed to move objects from PostgreSQL's default schema "public" to another schema. I found this post which shows how to move tables which was great, but I also need to move the functions.

Postgres 12 or newer

ALTER ROUTINE to cover both FUNCTION and PROCEDURE (added with pg 12).

DO
$do$
DECLARE
   _qry text;
BEGIN
   SELECT INTO _qry
          string_agg(format('ALTER ROUTINE public.%I(%s) SET SCHEMA new_schema;'  -- !
                   , p.proname, pg_get_function_identity_arguments(p.oid)), E'\n')
   FROM   pg_proc p
   JOIN   pg_namespace n ON n.oid = p.pronamespace
   WHERE  nspname = 'public';
      --  more filters?

   RAISE NOTICE '%', _qry;  -- inspect query string before executing
   -- EXECUTE _qry;         -- un-comment to execute
END
$do$;

The rest still applies:

Postgres 11 or older (original answer)

Refine the loop some more (demonstrating only the second query):

DO
$do$
DECLARE
   r   record;
   _qry text = '';
BEGIN
   FOR r IN
      SELECT p.proname, pg_get_function_identity_arguments(p.oid) AS params
      FROM   pg_proc p
      JOIN   pg_namespace n ON n.oid = p.pronamespace
      WHERE  nspname = 'public'
      --  more filters?
   LOOP
      _qry := _qry || format(E'\nALTER FUNCTION public.%I(%s) SET SCHEMA new_schema;'
                           , r.proname, r.params);
   END LOOP;

   RAISE NOTICE '%', _qry;  -- inspect query string before executing
   -- EXECUTE _qry;         -- un-comment to execute
END
$do$;

Remove unneeded tables from FROM.

concat() may be overkill, but format() simplifies the syntax.

Better set-based alternative

Re-casting the problem as set-based operation is more elegant. One SELECT with string_agg() does the job:

DO
$do$
DECLARE
   _qry text;
BEGIN
   SELECT INTO _qry
          string_agg(format('ALTER FUNCTION public.%I(%s) SET SCHEMA new_schema;'
                   , p.proname, pg_get_function_identity_arguments(p.oid)), E'\n')
   FROM   pg_proc p
   JOIN   pg_namespace n ON n.oid = p.pronamespace
   WHERE  nspname = 'public';
      -- and other conditions, if needed

   RAISE NOTICE '%', _qry;  -- inspect query string before executing
   -- EXECUTE _qry;         -- un-comment to execute
END
$do$;