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I am working on a Tkinter calculator, and I decided to add memory buttons. The M+ button adds to the memory, and M is supposed to fill the result box with the memory. I added a print statement after M+, so that once it is clicked, I confirm that the mem variable has value, yet it still gives me an error saying mem was referenced before assignment. Here is the part of the source giving me trouble:

Code:
elif key == 'M+':

    mem = result.get()

    print mem

    result.delete(0, END)

elif key == 'M':

    result.insert(END, mem)

And here is the full source.

Code:
from Tkinter import *

class calc(Frame):

    def __init__(self):

        global result

        top = Tk()

        top.title('UberCalc v2.0')

        Frame.__init__(self)

        result = Entry()

        result.pack(side=TOP)

        buttons = ['M+', 'M', '+/-', '1', '2', '3','4', '5', '6','7', '8', '9','.', '0', 'Clear']

        operbtn = ['-','+', '*','/', '=']

        ro = 1

        col = 0

        for x in buttons:

            action = lambda y=x: onclick(y)

            Button(self, text=x, width=5, relief='ridge', command=action).grid(row=ro, column=col)

            col += 1

            if col > 2:

                col = 0

                ro += 1

        col = 4

        ro = 1

        for x in operbtn:

            action = lambda y=x:onclick(y)

            Button(self, text=x, width=5, relief='ridge', command=action).grid(row=ro, column=col)

            ro += 1

        def onclick(key):

            global result

            if key == '=':

                try:

                    fetch = result.get()

                    answer = eval(fetch)

                    result.delete(0, END)

                    result.insert(0, answer)

                except(ZeroDivisionError):

                    result.delete(0,  END)

                    result.insert(0,  'Do not divide by zero please')

                except(SyntaxError):

                    result.delete(0,  END)

                    result.insert(0,  '0')

            elif key == 'Clear':

                result.delete(0, END)

            elif key == 'M+':

                mem = result.get()

                result.delete(0, END)

            elif key == 'M':

                result.insert(END, mem)

            elif key == '+/-':

                if result.get()[0] == '-':

                    result.delete(0)

                else:

                    result.insert(0, '-')

            else:

                result.insert(END, key)

if __name__ == '__main__':

    window = calc()

    window.pack()

    window.mainloop()

And finally, here is the error message:

Python Wrote:Exception in Tkinter callback
Traceback (most recent call last):
File "F:\Python26\lib\lib-tk\Tkinter.py", line 1410, in __call__
return self.func(*args)
File "F:\Documents and Settings\Administrator\Desktop\Coding\Python\My Projects\Under Development\GUI\Advanced_Calc.py", line 16, in <lambda>
action = lambda y=x: onclick(y)
File "F:\Documents and Settings\Administrator\Desktop\Coding\Python\My Projects\Under Development\GUI\Advanced_Calc.py", line 49, in onclick
result.insert(END, mem)
UnboundLocalError: local variable 'mem' referenced before assignment

If anyone could lend some assistance I would be very grateful Blackhat

I have solved the problem, I simply added

Code:
mem = ''

at the top of the script and then in my click function I added:

Code:
global mem

And it seems to work, view the completed source, look here

yeah, because if key equaled M+ "mem" would be initalized, however if M was hit first, you would run into problems, etc.

uber1337

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