conn = psycopg2.connect("dbname='{dbname}' user='{username}' host='localhost' password='{dbpass}'".format(
        dbname=dbname, username=user_name, dbpass=current_password)

cur = conn.cursor()

update_password_query = """ALTER USER my_user WITH PASSWORD %(password)s"""
cur.execute(update_password_query, {"password": new_password})

conn.commit()