Executing Postgresql function from Python - postgresql

Question

I have created a function (taken from wiki.postgresql.org) in my db for getting approximate row count.
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
$func$;
When I use the function from the psql cli, it works fine.
db=> SELECT count_estimate('SELECT * FROM schema.table_name');
count_estimate
----------------
4
(1 row)
However, when I run it from Python, using either SQLalchemy core or psycopg2, it gives an error.
conn.autocommit = True
cursor = conn.cursor()
cursor.execute("SELECT count_estimate('SELECT * FROM schema.table_name');")
conn.commit()
conn.close()
Error output
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.
How can I run the raw sql to get the function output?