### Basic Calculator using Python GUI (Tkinter) Program

This is a simple graphical user interfaced (GUI) Python application designed using Tkinter package to perform basic arithmetic calculations such as addition, subtraction, multiplication, and division of two numbers through the mouse click event. Copy an icon image ‘favicon.ico’ to the working directory to change the default icon in the title bar of the application.

### Introduction to Python Tkinter

In Python, the tkinter package (“Tcl/Tk interface”) is the standard interface to the Tk GUI toolkit. Both Tk and tkinter are available on most Unix platforms, as well as on Windows systems. (*Tk itself is not part of Python*; it is maintained at ActiveState.) You can check that tkinter is properly installed on your system by running `python -m tkinter`

from the command line; this should open a window demonstrating a simple Tk interface. For more details, refer to the official site of Python (python.org).

#### Source Code

```
# calc.py - a Python calculator
from tkinter import *
# the main class
class Calc():
def __init__(self):
self.total = 0
self.current = ""
self.new_num = True
self.op_pending = False
self.op = ""
self.eq = False
def num_press(self, num):
self.eq = False
temp = text_box.get()
temp2 = str(num)
if self.new_num:
self.current = temp2
self.new_num = False
else:
if temp2 == '.':
if temp2 in temp:
return
self.current = temp + temp2
self.display(self.current)
def calc_total(self):
self.eq = True
self.current = float(self.current)
if self.op_pending == True:
self.do_sum()
else:
self.total = float(text_box.get())
def display(self, value):
text_box.delete(0, END)
text_box.insert(0, value)
def do_sum(self):
if self.op == "add":
self.total += self.current
if self.op == "minus":
self.total -= self.current
if self.op == "times":
self.total *= self.current
if self.op == "divide":
self.total /= self.current
self.new_num = True
self.op_pending = False
self.display(self.total)
def operation(self, op):
self.current = float(self.current)
if self.op_pending:
self.do_sum()
elif not self.eq:
self.total = self.current
self.new_num = True
self.op_pending = True
self.op = op
self.eq = False
def cancel(self):
self.eq = False
self.current = "0"
self.display(0)
self.new_num = True
def all_cancel(self):
self.cancel()
self.total = 0
def sign(self):
self.eq = False
self.current = -(float(text_box.get()))
self.display(self.current)
sum1 = Calc()
root = Tk()
calc = Frame(root)
calc.grid()
root.title("Calculator")
root.wm_iconbitmap('favicon.ico')
root.resizable(width=FALSE, height=FALSE)
text_box = Entry(calc, justify = RIGHT, bd = 2, fg = "black")
text_box.grid(row = 0, column = 0, columnspan = 4, pady = 5)
text_box.insert(0, "0")
# make the buttons
numbers = "789456123"
i = 0
bttn = []
for j in range(1,4):
for k in range(3):
bttn.append(Button(calc, text = numbers[i], width=3, height=1))
bttn[i].grid(row = j, column = k, padx = 5, pady = 5)
bttn[i]["command"] = lambda x = numbers[i]: sum1.num_press(x)
i += 1
bttn_0 = Button(calc, text = "0", width=3, height=1)
bttn_0["command"] = lambda: sum1.num_press(0)
bttn_0.grid(row = 4, column = 0, padx = 5, pady = 5)
bttn_div = Button(calc, text = chr(247), width=3, height=1)
bttn_div["command"] = lambda: sum1.operation("divide")
bttn_div.grid(row = 1, column = 3, padx = 5, pady = 5)
bttn_off = Button(calc, text = "OFF", width=3, height=1)
bttn_off["command"] = root.destroy
bttn_off.grid(row = 5, column = 0, padx = 5, pady = 5)
bttn_mult = Button(calc, text = chr(215), width=3, height=1)
bttn_mult["command"] = lambda: sum1.operation("times")
bttn_mult.grid(row = 2, column = 3, padx = 5, pady = 5)
minus = Button(calc, text = "-", width=3, height=1)
minus["command"] = lambda: sum1.operation("minus")
minus.grid(row = 3, column = 3, padx = 5, pady = 5)
point = Button(calc, text = ".", width=3, height=1)
point["command"] = lambda: sum1.num_press(".")
point.grid(row = 4, column = 1, padx = 5, pady = 5)
add = Button(calc, text = "+", width=3, height=1)
add["command"] = lambda: sum1.operation("add")
add.grid(row = 4, column = 3, padx = 5, pady = 5)
neg= Button(calc, text = chr(177), width=3, height=1)
neg["command"] = sum1.sign
neg.grid(row = 5, column = 3, padx = 5, pady = 5)
clear = Button(calc, text = "C", width=3, height=1)
clear["command"] = sum1.cancel
clear.grid(row = 5, column = 1, padx = 5, pady = 5)
all_clear = Button(calc, text = "AC", width=3, height=1)
all_clear["command"] = sum1.all_cancel
all_clear.grid(row = 5, column = 2, padx = 5, pady = 5)
equals = Button(calc, text = "=", width=3, height=1)
equals["command"] = sum1.calc_total
equals.grid(row = 4, column = 2, padx = 5, pady = 5)
root.mainloop()
```

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