Code for GUI Calculator in Python [Explained in Detail]

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Code for GUI Calculator in Python [Explained in Detail]

Code for GUI Calculator in Python [Explained in Detail]

In this tutorial, I am sharing code to create a simple basic calculator to add, subtract, divide and multiply two numbers. GUI calculator in Python takes the two numbers as inputs from the user, perform arithmetic operation and display the result on Graphical User Inteface (GUI).

In an earlier article, I have shared a Python complete basic tutorial for beginner. That article is featured with the simple command line code by which you can add, subtract, divide and multiply two numbers using commands.

command line Python Calculator

This is like command line calculator in Python. But…

How to make GUI Calculator in Python?

The intention of the tutorial is not only to make the Calculator but also to understand the how GUI objects are created in Python.

At the end of this tutorial, I will share the complete code for Python calculator. You can copy-paste and use it.

If your intention is to learn the Python, just don’t copy the code. Follow this article step by step, you can write your own code. Trust me you will learn something amazing.

So let’s start.

For creating GUI, we are using PyQt4.QtGui package. It provides inbuilt functionality to create GUI objects like text area, button, labels…

If you don’t have PyQt4.QtGui package installed on your system, you can download and install with this simple command.

sudo apt-get install python-qt4

Let’s start by considering the requirement to create calculator…

For our code to make the calculator, we need…

  • 2 text fields to take the user inputs
  • 4 buttons to perform four different arithmetic operations like add, subtract, divide and multiply
  • 1 label is to display the result

GUI Calculator in Python output

How to create these GUI objects in Python?

Code for Creating text field for user input

txtArea1 = QLineEdit("", widget)
txtArea2 = QLineEdit("", widget)

Code for Creating Clickable GUI buttons

btnAdd = QPushButton("Add", widget)
btnSub = QPushButton("Subtract", widget)
btnDiv = QPushButton("Divide", widget)
btnMul = QPushButton("Multiply", widget)

Python Code for Plotting GUI objects in Widget

There is one widget, inside which we are displaying all the GUI objects.

To display the objects in the widget, we have to position them using…

  • widget.resize()
  • widget.move()

All the GUI objects will be configured inside the init() function. It is the first function to be called.

Based on the button user clicks on, it will call the respective function.

For example, if the user clicks on the multiplication button, it calls multiplication() function. It reads the value from two text fields and performs the multiplication operation.

Reading User Input Values from Text Field:

The value in input text field is in the text format and you need to convert it into an integer before performing arithmetic operations.

This is a simple line of Python code we are using to convert text to an integer.

num1 = int(txtArea1.text())
num2 = int(txtArea2.text())

Performing Arithmetic Operation Based on User Input:

Perform the arithmetic operation on user input num1 and num2 is pretty easy.

Write a dedicated function for each of the arithmetic operation. These functions return the output to the caller.

Display Python Calculator Result:

Assign the output to the label object using label.setText().

label.setText("Output: "+str(num1 * num2))

That’s it. If you take the other programming languages, it is not so much easy to create GUI, but the Python does it with ease.
Now here it is you are looking for…

Code for GUI Calculator in Python

Simply copy and save it in python file. Run it.

import sys
from PyQt4.QtGui import *
#from PyQt4 import QtGui

app = QApplication(sys.argv)
widget = QWidget()
label = QLabel("", widget)

btnAdd = QPushButton("Add", widget)
btnSub = QPushButton("Subtract", widget)
btnDiv = QPushButton("Divide", widget)
btnMul = QPushButton("Multiply", widget)


#txtArea = QPlainTextEdit("Text To Edit", widget)widget.resize

txtArea1 = QLineEdit("", widget)
txtArea2 = QLineEdit("", widget)

def init():

    widget.resize(300, 300)
    widget.move(300, 300)
    widget.setWindowTitle('Calculator')
    widget.show()

    txtArea1.move(20,10)
    txtArea1.show()
    txtArea2.move(20,60)
    txtArea2.show()

    label.setText("")
    label.move(20,110)
    label.show()

    btnAdd.setToolTip('Addition')
    btnAdd.move(20,160)
    btnAdd.clicked.connect(addition)
    btnAdd.show()

    btnSub.setToolTip('Subtraction')
    btnSub.move(110,160)
    btnSub.clicked.connect(subtraction)
    btnSub.show()

    btnDiv.setToolTip('Division')
    btnDiv.move(20,210)
    btnDiv.clicked.connect(division)
    btnDiv.show()

    btnMul.setToolTip('Multiplication')
    btnMul.move(110,210)
    btnMul.clicked.connect(multiplication)
    btnMul.show()


def addition():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Addition: "+str(num1 + num2))

def subtraction():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Subtraction: "+str(num1 - num2))

def multiplication():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Multiplication: "+str(num1 * num2))

def division():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Division: "+str(num1 / num2))

if __name__ == "__main__":
     init()

app.exec_()

You can modify the field in the code to understand and enhance the GUI for the calculator.

You can enhance this calculator by various ways…

  • Add numeric button so that you can get the values by clicking on the button instead of manually typing in the text area.
  • Add more arithmetic operation such as log, trigonometric function. Write a separate function for each operation and set one button for each operation.

If you want to be an expert in the Python, do read our Python tutorial which is available FREE for all.

Now, this is all for you. Get your hands dirty with code and show your skill. If you have any question related to GUI Calculator in Python, write in a comment.

Happy Pythoning!

Aniruddha Chaudhari

Aniruddha Chaudhari

I am complete Python Nut, love Linux and vim as an editor. I hold a Master of Computer Science from NIT Trichy. I dabble in C/C++, Java too. I keep sharing my coding knowledge and my own experience on <b>CSEstack.org</b> portal.

23 Comments

  3. Sir your tutorial is very explicit. my question is: it is not possible to use the mouse to drag n design those widgets (controls) on the form like what is obtainable in VB 6.0 and VB.net before one start coding in Python?

    Am new in Python pls reply…

    Best Regards.

    Reply

    2. You can simply use the QT designer tool for creating the graphical basement of your program.
      for the next step you should convert your QT file (with name.ui format ) to python file (name.py) & then start writing codes for everything that needs.

      Reply

  4. Hi Aniruddha,

    I had gone through the GUI Calculator tutorial Explanation is good

    I tried to install it in Windows 10 in python 3.6.6

    for that, I Installed “pip install PyQt5” module

    then I am getting “NameError: name ‘QWidget’ is not defined” error

    can you please check and give me the solution

    Reply
  5. import sys
from PyQt5.QtGui import *
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *

# from PyQt4 import QtGui
app = QApplication(sys.argv)
widget = QWidget()
label = QLabel("", widget)

btnAdd = QPushButton("Add", widget)
btnSub = QPushButton("Subtract", widget)
btnDiv = QPushButton("Divide", widget)
btnMul = QPushButton("Multiply", widget)

# txtArea = QPlainTextEdit("Text To Edit", widget)widget.resize

txtArea1 = QLineEdit("", widget)
txtArea2 = QLineEdit("", widget)


def init():
    widget.resize(300, 300)
    widget.move(300, 300)
    widget.setWindowTitle('Calculator')
    widget.show()

    txtArea1.move(20, 10)
    txtArea1.show()
    txtArea2.move(20, 60)
    txtArea2.show()

    label.setText("")
    label.move(20, 110)
    label.show()

    btnAdd.setToolTip('Addition')
    btnAdd.move(20, 160)
    btnAdd.clicked.connect(addition)
    btnAdd.show()

    btnSub.setToolTip('Subtraction')
    btnSub.move(110, 160)
    btnSub.clicked.connect(subtraction)
    btnSub.show()

    btnDiv.setToolTip('Division')
    btnDiv.move(20, 210)
    btnDiv.clicked.connect(division)
    btnDiv.show()

    btnMul.setToolTip('Multiplication')
    btnMul.move(110, 210)
    btnMul.clicked.connect(multiplication)
    btnMul.show()


def addition():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Addition: " + str(num1 + num2))


def subtraction():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Subtraction: " + str(num1 - num2))


def multiplication():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Multiplication: " + str(num1 * num2))


def division():
    num1 = int(txtArea1.text())
    num2 = int(txtArea2.text())
    label.setFixedWidth(200)
    label.setText("Division: " + str(num1 / num2))


if __name__ == "__main__":
    init()

app.exec_()
    Reply
  6. from PyQt5.QtGui import *

    Getting this error.

    ImportError: DLL load failed while importing QtGui: The specified module could not be found.

    so imported in this way
    import PyQt5
    Now it is throwing me

    app = QApplication(sys.argv)
NameError: name 'QApplication' is not defined

    Kindly, can you suggest me what to do?
    I have used pip install python-qt5

    Reply

    1. I think you are using a Windows operating system.
      Looks like python3.dll is missing from your installed Python files. Check if it is there. If it is there and you are using virtual environment, copy python3.dll file from c:\python35 (your installed Python directory) to virtualenv\scripts\python3.dll.

      Reply

  7. I have this python code for a GUI calculator but need someone who could tell me how to get lambda out of the program from Tkinter import *

    def iCalc(source, side):
    storeObj = Frame(source, borderwidth=4, bd=4, bg="powder blue")
    storeObj.pack(side=side, expand =YES, fill =BOTH)
    return storeObj

def button(source, side, text, command=None):
    storeObj = Button(source, text=text, command=command)
    storeObj.pack(side=side, expand = YES, fill=BOTH)
    return storeObj

class app(Frame):
    def __init__(self):
        Frame.__init__(self)
        self.option_add('*Font', 'arial 20 bold')
        self.pack(expand = YES, fill =BOTH)
        self.master.title('Calculator')

        display = StringVar()
        Entry(self, relief=RIDGE, textvariable=display,
          justify='right'
          , bd=30, bg="powder blue").pack(side=TOP,
                                          expand=YES, fill=BOTH)

        for clearButton in (["C"]):
            erase = iCalc(self, TOP)
            for ichar in clearButton:
                button(erase, LEFT, ichar, lambda
                    storeObj=display, q=ichar: storeObj.set(''))

        for numButton in ("789/", "456*", "123-", "0.+"):
         FunctionNum = iCalc(self, TOP)
         for iEquals in numButton:
            button(FunctionNum, LEFT, iEquals, lambda
                storeObj=display, q=iEquals: storeObj
                   .set(storeObj.get() + q))

        EqualButton = iCalc(self, TOP)
        for iEquals in "=":
            if iEquals == '=':
                btniEquals = button(EqualButton, LEFT, iEquals)
                btniEquals.bind('', lambda e,s=self,
                    storeObj=display: s.calc(storeObj), '+')


            else:
                btniEquals = button(EqualButton, LEFT, iEquals,
                   lambda storeObj=display, s=' %s ' % iEquals: storeObj.set
                   (storeObj.get() + s))

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


if __name__=='__main__':
 app().mainloop()
    Reply

      1. Can you give me an example of what one of the lambda codes would look if it was a typical function? I am a high school student taking a college class and this assignment was given to me in place of an assignment because my grandpa was in the hospital and all I just can’t seem to understand. Was doing good in the class until they did the stay at home order?

        Reply

  8. Can you give me a example of what one of the codes would look like. For some reason it is just not clicking with me

    Reply

  9. Please excuse my ignorance but when I enter “sudo apt-get install python-qt4” in python shell, it returns an error. Did you specify how to acquire this package and I missed it?

    Reply

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