I think all you need to do is remove the () from your connect function calls, so get_node("Button").connect("button_down",self,"_on_button_pressed()") becomes get_node("Button").connect("button_down",self,"_on_button_pressed").
On an aside,to use the code block thingy on the forums you just need to encapsulate anything you want to treat as code in ` (the key next to the number 1 on my keyboard) and it will be converted/rendered to look like code.