Why the values are not retreived?

worst_gui_api_ever.py

panel = nuke.Panel("Create")

panel.addSingleLineInput("start", int(nuke.root()["first_frame"].getValue()))
panel.addSingleLineInput("finish", int(nuke.root()["last_frame"].getValue()))
panel.addSingleLineInput("step", int(nuke.root().fps()))
panel.addButton("Create")

obscure_status_int = panel.show()

# The API called "get value of the field by providing it's UI label" earns the
# mark of the most fucked up disgusting crap engineering ever (tm)
start = panel.value("start")
finish = panel.value("finish")
istep = panel.value("step")

nuke.message(str([start, finish, istep]))