Postgres: INSERT if does not exist already

I'm using Python to write to a postgres database: ``` sql_string = "INSERT INTO hundred (name,name_slug,status) VALUES (" sql_string += hundred + ", '" + hundred_slug + "', " + status + ");" cursor.execute(sql_string) ``` But because some of my rows are identical, I get the following error: ``` psycopg2.IntegrityError: duplicate key value violates unique constraint "hundred_pkey" ``` How can I write an 'INSERT unless this row already exists' SQL statement? I've seen complex statements like this recommended: ``` IF EXISTS (SELECT * FROM invoices WHERE invoiceid = '12345') UPDATE invoices SET billed = 'TRUE' WHERE invoiceid = '12345' ELSE INSERT INTO invoices (invoiceid, billed) VALUES ('12345', 'TRUE') END IF ``` But firstly, is this overkill for what I need, and secondly, how can I execute one of those as a simple string?