Calculator_Program

Calculator Program in Python

Today, we are going to build a Python Calculator using Tkinter with easy to understand steps.

The python calculator which we are going to build will look something like this:

Python Calculator Project

Step 1: Importing the necessary modules

from tkinter import *
import parser
from math import factorial

Step 2: Making a window

root = Tk()
root.title("Calculator - SON BK")

Step 3: Designing the buttons

Input:

display = Entry(root)
display.grid(row=1, columnspan=6, sticky=N + E + W + S)

Buttons:

Button(root, text="1", command=lambda: get_variables(1)).grid(row=2, column=0, sticky=N + S + E + W)
Button(root, text="2", command=lambda: get_variables(2)).grid(row=2, column=1, sticky=N + S + E + W)
Button(root, text="3", command=lambda: get_variables(3)).grid(row=2, column=2, sticky=N + S + E + W)

Button(root, text="4", command=lambda: get_variables(4)).grid(row=3, column=0, sticky=N + S + E + W)
Button(root, text="5", command=lambda: get_variables(5)).grid(row=3, column=1, sticky=N + S + E + W)
Button(root, text="6", command=lambda: get_variables(6)).grid(row=3, column=2, sticky=N + S + E + W)

Button(root, text="7", command=lambda: get_variables(7)).grid(row=4, column=0, sticky=N + S + E + W)
Button(root, text="8", command=lambda: get_variables(8)).grid(row=4, column=1, sticky=N + S + E + W)
Button(root, text="9", command=lambda: get_variables(9)).grid(row=4, column=2, sticky=N + S + E + W)

# adding other buttons to the calculator
Button(root, text="AC", command=lambda: clear_all()).grid(row=5, column=0, sticky=N + S + E + W)
Button(root, text="0", command=lambda: get_variables(0)).grid(row=5, column=1, sticky=N + S + E + W)
Button(root, text=".", command=lambda: get_variables(".")).grid(row=5, column=2, sticky=N + S + E + W)

Button(root, text="+", command=lambda: get_operation("+")).grid(row=2, column=3, sticky=N + S + E + W)
Button(root, text="-", command=lambda: get_operation("-")).grid(row=3, column=3, sticky=N + S + E + W)
Button(root, text="*", command=lambda: get_operation("*")).grid(row=4, column=3, sticky=N + S + E + W)
Button(root, text="/", command=lambda: get_operation("/")).grid(row=5, column=3, sticky=N + S + E + W)

# adding new operations
Button(root, text="pi", command=lambda: get_operation("*3.14")).grid(row=2, column=4, sticky=N + S + E + W)
Button(root, text="%", command=lambda: get_operation("%")).grid(row=3, column=4, sticky=N + S + E + W)
Button(root, text="(", command=lambda: get_operation("(")).grid(row=4, column=4, sticky=N + S + E + W)
Button(root, text="exp", command=lambda: get_operation("**")).grid(row=5, column=4, sticky=N + S + E + W)

Button(root, text="<-", command=lambda: undo()).grid(row=2, column=5, sticky=N + S + E + W)
Button(root, text="x!", command=lambda: fact()).grid(row=3, column=5, sticky=N + S + E + W)
Button(root, text=")", command=lambda: get_operation(")")).grid(row=4, column=5, sticky=N + S + E + W)
Button(root, text="^2", command=lambda: get_operation("**2")).grid(row=5, column=5, sticky=N + S + E + W)
Button(root, text="^2", command=lambda: get_operation("**2")).grid(row=5, column=5, sticky=N + S + E + W)
Button(root, text="=", command=lambda: calculate()).grid(columnspan=6, sticky=N + S + E + W)

Explanation:

In this calculator program in python, the "Entry" function helps in making a text input field and we use .grid() method to define the positioning associated with the button or input field. We use the button method to display a button on our application window.

root – the name with which we refer to our window
text – text to be displayed on the button
row – row index of the grid
column – column index of the grid
columnspan – spans or combines the number of columns
sticky – If the resulting cell is larger than the widget then sticky defines how to expand the widget. The combination of constants used S, N, E, and W, or NW, NE, SW, and SE are analogous to the directions in compass. N+E+W+S means that the widget should be expanded in all directions.

NOTE:

If you have noticed an error such as no function get_variable() found, then do not worry. We are just defining an action function associated with each button. Since we have just called and not declared them yet hence the error. Now, lets defined those functions.

To connect the digit button to the get_variable() function, we use the "command" parameter. Here we pass '1' as an argument to the get_variable() function when button '1' is pressed.

Step 4: Mapping the buttons

Mapping the digits

 # i keeps the track of current position on the input text field
 i = 0
 # Receives the digit as parameter and display it on the input field
 def get_variables(num):
     global i
     display.insert(i, num)
     i += 1

The get_variable() function receives the digit as parameter. The digit is inserted to the input field with .insert() method with parameters ‘i’ and ‘num’. The global variable i is incremented each time to get updated with the position to insert the next digit or next operator.

i – the position to insert the digit
num – the digit

Mapping the operator buttons

 def get_operation(operator):
     global i
     length = len(operator)
     display.insert(i, operator)
     i += length

The get_operation() function receives the operator as a parameter which is then inserted to the text field at the ith position of python calculator.

Mapping the AC button

 def clear_all():
     display.delete(0, END)

We use the .delete() method to remove characters in the text field. It accepts the start and end position as the parameter.

0 – start position
END – end position

Mapping the undo button

 def undo():
     entire_string = display.get()
     if len(entire_string):
        new_string = entire_string[:-1]
        clear_all()
        display.insert(0, new_string)
     else:
        clear_all()
        display.insert(0, "Error")

We use the .get() method to fetch the string present on the input field. If there is really a string present, we slice out the last character, clear the input field and push the new string back to the input field which does not contain the last character.

Mapping the ‘= ’ button

 def calculate():
     entire_string = display.get()
     try:
        a = parser.expr(entire_string).compile()
        result = eval(a)
        clear_all()
        display.insert(0, result)
    except Exception:
        clear_all()
        display.insert(0, "Error")

We fetch the string present on the input field using the .get() method. We now use the parse module to scan the string with the help of .expr() method which accepts the string as a parameter. We basically leave it to the parser to build an abstract syntax tree of the string which is evaluated using the eval() function.

Once we get the result, we push it to the input field after clearing it.

Mapping the factorial key

 def fact():
     entire_string = display.get()
     try:
        result = factorial(int(entire_string))
        clear_all()
        display.insert(0, result)
     except Exception:
        clear_all()
        display.insert(0, "Error")

Finish

  root.mainloop()

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