raceback (most recent call last):
File "C:/Python32/n", line 1, in <module>

from Tkinter import *

# button text list
cmdlst = ['7', '8', '9', '+', '%',
          '4', '5', '6', '-', '**',
          '1', '2', '3', '*', '//',
          '.', '0', 'CL', '/', '=']

class MyButton(Button):

    backref = None

    def Click(self):
        # back reference
        self.backref.BtnCmd(self["text"])


class CalcApp:

    def __init__(self, master):
        frame = Frame(master)

        self.textbox = Entry(width=30, takefocus=1)
        self.textbox.pack(side=TOP)
        self.textbox.focus_force()

        self.buttons = []
        for n, c in enumerate(cmdlst):
            self.buttons.append(MyButton(frame, text=c, width=5))
            self.buttons[n]["command"] = self.buttons[n].Click
            self.buttons[n].backref = self
            self.buttons[n].grid(row=n/5, column=n%5)

        frame.pack()

    def BtnCmd(self, cmd):
        if cmd == '=':
            try:
                res = eval(self.textbox.get())
            except:
                res = "Error!"
            self.textbox.delete(0, END)
            self.textbox.insert(0, str(res))
        elif cmd == 'CL':
            self.textbox.delete(0, END)
        else:
            self.textbox.insert(END, cmd)

root = Tk()
root.title("EWCalc")

calcapp = CalcApp(root)
root.mainloop()

i fix it but now it came out
Traceback (most recent call last):

File "C:/Python32/n", line 52, in <module>
    calcapp = CalcApp(root)
  File "C:/Python32/n", line 32, in __init__
    self.buttons[n].grid(row=n/5, column=n%5)
  File "C:\Python32\lib\tkinter\__init__.py", line 1887, in grid_configure
    + self._options(cnf, kw))
_tkinter.TclError: bad row value "0.0": must be a non-negative integer
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