从 Python 执行 Postgresql 函数

我在数据库中创建了一个函数（取自 wiki.postgresql.org），用于获取近似行数。

CREATE FUNCTION ais_history.count_estimate(query text)
        RETURNS integer
        LANGUAGE plpgsql AS
        $func$
                DECLARE
                        rec   record;
                        rows  integer;
                BEGIN
                FOR rec IN EXECUTE 'EXPLAIN ' || query LOOP
                        rows := substring(rec."QUERY PLAN" FROM ' rows=([[:digit:]]+)');
                        EXIT WHEN rows IS NOT NULL;
                END LOOP;

                RETURN rows;
                END
        $func$;

当我使用 psql cli 中的函数时，它工作正常。

db=> SELECT count_estimate('SELECT * FROM schema.table_name');
 count_estimate
----------------
              4
(1 row)

但是，当我使用 SQLalchemy core 或 psycopg2 从 Python 运行它时，它会出现错误。

conn.autocommit = True
cursor = conn.cursor()
cursor.execute("SELECT count_estimate('SELECT * FROM schema.table_name');")
conn.commit()
conn.close()

错误输出

UndefinedFunction                         Traceback (most recent call last)
Input In [91], in <cell line: 8>()
      5 conn.autocommit = True
      6 cursor = conn.cursor()
----> 8 cursor.execute("SELECT count_estimate('SELECT * FROM schema.table_name');")
     10 conn.commit()
     11 conn.close()

UndefinedFunction: function count_estimate(unknown) does not exist
LINE 1: SELECT count_estimate('SELECT * FROM schema.table_name...
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

如何运行原始 sql 来获取函数输出？