Transaction persistence between execute() calls

I need that 5 queries fired by the same ajax request to a web python
application see the same database snapshot and i don't understand how
exactly to do it. Could it be like this:?

import psycopg2 as db
dsn = 'host=localhost dbname=dbname user=user password=passwd'
connection = db.connect(dsn)
cursor = connection.cursor()

cursor.execute('BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;');
rs1 = cursor.execute(query_1, (param1,))
rs2 = cursor.execute(query_2, (param2,))
cursor.execute('COMMIT;');

cursor.close()
connection.close()

Or:

cursor.execute('BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;');
rs1 = cursor.execute(query_1, (param1,))
rs2 = cursor.execute(query_2, (param2,))

cursor.close()
connection.commit()
connection.close()

Or something else? BTW i can't find the html doc with all the classes.
Where is it?

Regards, Clodoaldo Pinto Neto