psycopg2: insert multiple rows with one query

I need to insert multiple rows with one query (number of rows is not constant), so I need to execute query like this one:

INSERT INTO t (a, b) VALUES (1, 2), (3, 4), (5, 6);

The only way I know is

args = [(1,2), (3,4), (5,6)]
args_str=",".join(cursor.mogrify("%s", (x, )) for x in args)
cursor.execute("INSERT INTO t (a, b) VALUES "+args_str)

but I want some simpler way.