Calculator Explanation

[Fadili]

from Tkinter import *
 
def frame(root, side): 
    w = Frame(root)
    w.pack(side=side, expand=YES, fill=BOTH)
    return w
 
def button(root, side, text, command=None): 
    w = Button(root, text=text, command=command) 
    w.pack(side=side, expand=YES, fill=BOTH)
    return w
 
class Calculator(Frame):
    def __init__(self):
        Frame.__init__(self)
        self.option_add('*Font', 'Verdana 12 bold')
        self.pack(expand=YES, fill=BOTH)
        self.master.title('Simple Calculator')
        self.master.iconname("calc1")
 
        display = StringVar()
        Entry(self, relief=SUNKEN, textvariable=display).pack(side=TOP, expand=YES, fill=BOTH)
 
        for key in ("123", "456", "789", "-0."):
            keyF = frame(self, TOP)
            for char in key:
                button(keyF, LEFT, char,
                       lambda w=display, c=char: w.set(w.get() + c))
 
        opsF = frame(self, TOP)
        for char in "+-*/=":
            if char == '=':
                btn = button(opsF, LEFT, char)
                btn.bind('<ButtonRelease-1>',
                         lambda e, s=self, w=display: s.calc(w), '+')
            else:
                btn = button(opsF, LEFT, char,
                   lambda w=display, s=' %s '%char: w.set(w.get()+s))
 
        clearF = frame(self, BOTTOM)
        button(clearF, LEFT, 'Clr', lambda w=display: w.set(''))
 
    def calc(self, display):
        try:
            display.set('eval(display.get())')
        except:
            display.set("ERROR")
 
if __name__ == '__main__':
    Calculator().mainloop()

Who can explain the code? How are the buttons created?
Thanks

[bvdet]

That's why I like to import the module instead of importing everything.

import Tkinter
# or import Tkinter as Tk

You may be able to see that the buttons are created with the call

w = Tkinter.Button(root, text=text, command=command)

Then the pack geometry manager is called as a method of the widget to display the button.

w.pack(side=side, expand=YES, fill=BOTH)

display is the variable shown in the Tkinter.Entry widget. The current value of the variable can be obtained with the get() method of Tkinter variables. The "=" button is bound to the calc() function which evaluates the current value of display and sets the variable to the result using the set() method of Tlinter variables.

[bvdet]

To display a calculated result, method calc() should look like this:

    def calc(self, display):
        try:
            display.set(str(eval(display.get())))
        except:
            display.set("ERROR")

[Fadili]

Thanks bvdet, very clearly explained