Build Calculator using Python Tkinter – From Scratch to Pro | CodeHelping

Building a calculator using Python Tkinter is a great project. This blog will guide you through creating a basic GUI Calculator with Tkinter library, Python’s standard GUI toolkit.

How to Create Calculator using Python Tkinter

To create Calculator using Python Tkinter, we begin by importing tkinter and initializing the main window using <strong>root = Tk()</strong>.
The GUI window is sized using root.geometry("430x500").

from tkinter import * 

Then declare a global string, which will store the arithmetic expression entered by the user.

To handle user input, we define the setexpression() function that appends numbers or operators to the expression string and updates the entry field.

The c<strong>alculator()</strong> function uses Python’s built-in <strong>eval()</strong> to evaluate the expression and display the result. Errors (like incomplete expressions) are caught using a try-except block. The clear() function resets everything for a new calculation.

Let’s Build the Interface now!!

The layout is created using Entry and multiple Button widgets. Each button corresponds to a number or operator and calls the setexpression() function with the appropriate value.

Buttons like “=“ and “Clear” trigger their respective functions (calculator() and clear()).

The buttons are placed using the <strong>.grid()</strong> method, neatly organizing them into rows and columns for a familiar calculator layout.

Code to Create Calculator using Python Tkinter

# importing the tkinter module
from tkinter import *

# initializing the tkinter
root = Tk()

# setting the width and height of the gui calculator
root.geometry("430x500")    # x is small case here

# declaring an empty string variable
expression = ""

# defining function which will set expressions and answers to the  user
def setexpression(num):
    global expression
    expression = expression + str(num)
    value.set(expression)

# defining a function to calculate the expression entered by the user
def calculator():
    try:
        global expression
        answer = str(eval(expression))
        value.set(answer)
    except:
        value.set("Enter correct expression")
        expression = ""

# function to clear everything in expression
def clear():
    global expression
    expression = ""
    value.set(expression)

# declaring font variables as ("Language", size)
large_font = ('Verdana', 15)
small_font = ('Verdana', 10)

# declaring variable to take value of expression entered by the user
value = StringVar(value="Enter expression")

# entry widget to take expression from user and to show 
# calculations 
Entry(root, textvariable=value, font=large_font).grid(row=0, 
    column=0, columnspan=4, ipadx=70)

# Now, there are some most basic buttons which should be present 
# in a calculator
# here, each button is calling the setexpression function which 
# is used to set values in the entry widget entered by the user 
# on pressing the buttons 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, .
Button(root, text="+", fg="red", command=lambda: 
    setexpression("+"), height=4,width=8).grid(row=1,column=0,pady=10)
Button(root, text="-", fg="red", command=lambda:
    setexpression("-"), height=4, width=8).grid(row=2, column=0, pady=10)
Button(root, text="X", fg="red", command=lambda: 
    setexpression("*"), height=4, width=8).grid(row=3, column=0,pady=10)
Button(root, text="/", fg="red", command=lambda: 
    setexpression("/"), height=4, width=8).grid(row=4, column=0,pady=10)
Button(root, text="1", fg="red", command=lambda: 
    setexpression("1"), height=4, width=8).grid(row=1, column=1,pady=10)
Button(root, text="2", fg="red", command=lambda: 
    setexpression("2"), height=4, width=8).grid(row=1, column=2,pady=10)
Button(root, text="3", fg="red", command=lambda: 
    setexpression("3"), height=4, width=8).grid(row=1, column=3,pady=10)
Button(root, text="4", fg="red", command=lambda: 
    setexpression("4"), height=4, width=8).grid(row=2, column=1,pady=10)
Button(root, text="5", fg="red", command=lambda: 
    setexpression("5"), height=4, width=8).grid(row=2, column=2)
Button(root, text="6", fg="red", command=lambda: 
    setexpression("6"), height=4, width=8).grid(row=2, column=3,pady=10)
Button(root, text="7", fg="red", command=lambda: 
    setexpression("7"), height=4, width=8).grid(row=3, column=1,pady=10)
Button(root, text="8", fg="red", command=lambda: 
    setexpression("8"), height=4, width=8).grid(row=3, column=2,pady=10)
Button(root, text="9", fg="red", command=lambda: 
    setexpression("9"), height=4, width=8).grid(row=3, column=3,pady=10)
Button(root, text="0", fg="red", command=lambda: 
    setexpression("0"), height=4, width=8).grid(row=4, column=2,pady=10)
Button(root, text=".", fg="red", command=lambda: 
    setexpression("."), height=4, width=8).grid(row=4, column=1,pady=10)

# "=" button to call the calculator button which will return and 
# show the calculated value in the entry widget
Button(root, text="=", fg="red", command=calculator, height=4,
width=8).grid(row=4, column=3, pady=10)

# "Clear" button to call the clear function which will clear the 
# entry widget so that the user can start clculating again
Button(root, text="Clear", fg="red", command=clear, height=4, 
    width=20).grid(row=5, column=1, pady=10)

# .mainloop() is used when the code is ready to run
root.mainloop()

Output:

Conclusion: GUI Calculator in Python with Tkinter

Finally, <strong>root.mainloop()</strong> is used to run the application. Once executed, you’ll have a fully functional, beginner-friendly calculator with a graphical interface.

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