Can convert Tkinter inputs into numbers
Question: 
    __author__ = 'Feuer'
    from tkinter import *
    
    root = Tk()
    root.geometry("750x400")
    
    
    def stop():
        exit()
    
    
    def plus():
        global erg11
        erg11 = z1 + z2
    
    
    class Start:
        def __init__(self, master):
            frame = Frame(master)
            frame.pack()
    
            self.Label_1 = Label(frame, text="Bitte wählen Sie die Rechenart aus, die Sie benutzen möchten!")
            self.Label_2 = Label(frame, text="Addition")
            self.Label_3 = Label(frame, text="Subtraktion")
            self.Label_4 = Label(frame, text="Multiplikation")
            self.Label_5 = Label(frame, text="Division")
            self.Label_6 = Label(frame, text="Wurzel")
            self.Label_7 = Label(frame, text="Logarithmus")
            self.Button_1 = Button(frame, text="Go!", command=Add)
            self.Button_2 = Button(frame, text="Go!")
            self.Button_3 = Button(frame, text="Go!")
            self.Button_4 = Button(frame, text="Go!")
            self.Button_5 = Button(frame, text="Go!")
            self.Button_6 = Button(frame, text="Go!")
            self.Button_7 = Button(frame, text="Das Programm beenden!", command=stop)
    
            self.Label_1.grid(row=0, columnspan=2)
            self.Label_2.grid(row=1, column=0)
            self.Label_3.grid(row=2, column=0)
            self.Label_4.grid(row=3, column=0)
            self.Label_5.grid(row=4, column=0)
            self.Label_6.grid(row=5, column=0)
            self.Label_7.grid(row=6, column=0)
            self.Button_1.grid(row=1, column=1)
            self.Button_2.grid(row=2, column=1)
            self.Button_3.grid(row=3, column=1)
            self.Button_4.grid(row=4, column=1)
            self.Button_5.grid(row=5, column=1)
            self.Button_6.grid(row=6, column=1)
            self.Button_7.grid(row=7, columnspan=2)
    
    
    class Add:
        def __init__(self):
            newwin = Toplevel()
            newwin.geometry("750x400")
            frame2 = Frame(newwin)
            frame2.pack()
    
            global erg11
    
            global z1
            global z2
    
            erg11 = "Ready"
    
            self.Label_1 = Label(frame2, text="Additionsverfahren")
            self.Entry_1 = Entry(frame2)
            self.Label_2 = Label(frame2, text="+")
            self.Entry_2 = Entry(frame2)
            self.Label_3 = Label(frame2, text="=")
            self.Button_1 = Button(frame2, text="Zurück", command=newwin.destroy)
            self.Button_2 = Button(frame2, text="Ergebniss berechnen")
            self.Label_Erg1 = Label(frame2, text=erg11)
    
            self.Button_2.bind("<Button-1>", plus)
    
            self.Label_1.grid(row=0, columnspan=4)
            self.Entry_1.grid(row=1, column=0)
            self.Label_2.grid(row=1, column=1)
            self.Entry_2.grid(row=1, column=2)
            self.Label_3.grid(row=1, column=3)
            self.Button_2.grid(row=2, columnspan=4)
            self.Button_1.grid(row=3, columnspan=4)
            self.Label_Erg1.grid(row=1, column=4)
    
    
    
    
    
    
    
    
    
    app = Start(root)
    root.mainloop()
    

this is my code i am using at the moment.I try to create a little useless
calculator with gui in Python. I cant figure out how to get the variable (z1 /
z1) out of Entry_1 and _2 when someone is pressing the button_2 (in the second
class). Could any one sugesst me some code to fix it?

* * *

Edit:  
_I edited the Code, that everybody could try to find a solution for my
problem, because my solution approaches ended in a stalemate. (Ayres)_


Answer: The content of your entries are read immediately after creation of them,
leading `get()` to return an empty string that can't be converted.

The `get` method has to be called somewhere else, though I can't exactly say
when.

