Tkinker comand problem...

# Dice Roller Program
# By Evan Patterson

from Tkinter import *

class App:

    def __init__(self, master):

        frame = Frame(master)

        # Labels        
        self.label1 = Label(master, text="# of Rolls:")
        self.label2 = Label(master, text="# of Sides:")
        self.label3 = Label(master, text="Results:")
        self.label4 = Label(master, text="Dice Roller\n by Evan Patterson")
        self.label1.grid(sticky=E)
        self.label2.grid(sticky=E)
        self.label3.grid(sticky=E)
        self.label4.grid(row=0, column=2, columnspan=2, rowspan=2)

        # Entries
        self.entry1 = Entry(master)
        self.entry2 = Entry(master)
        self.results = Entry(master)
        self.entry1.grid(row=0, column=1)
        self.entry2.grid(row=1, column=1)
        self.results.grid(row=2, column=1)
    
        # Buttons
        self.exit = Button(master, text="Exit", command=master.quit)
        self.roll = Button(master, text="Roll!", command=self.roll)
        self.roll.grid(row=3, column=2)
        self.exit.grid(row=3, column=3)
        
        # Checkpoint
        self.rollopt = IntVar()
        checkbutton = Checkbutton(master, text="Don't Add Rolls Together", variable=self.rollopt , command=self.roll)
        checkbutton.grid(columnspan=2, column=0, row=3, sticky=W)
                       
    def roll(self):
        if rollopt == 0:
            rollr = random.randint(1, self.entry2)
        
root = Tk()
app = App(root)
root.title("Dice Roller")
root.mainloop()