Build a simple calculator using python and PyQt5

The full code of this project on git :https://github.com/Tejas-Achar/Simple-Calculator

Hi again!!

That root cause of writing this post is to have a glimpse of how UI development using python looks like.

The simplest application that I could think of, to demonstrate, is a simple calculator.

So lets dive in and see how to go about this.

Prerequisites :

1. PyQt5 [ pip install PyQt5 ]

2. Qt designer [ download from : https://tinyurl.com/yc3xmac5 ]

Once you setup PyQt5 and Qt designer, you're all set to go.

Before we start with the GUI, lets write a simple script, which performs the calculator operation.

1. Lets take user input of the equation ( Ex : 1+2*3 ) as a string

userInput = input("enter the equation here")

2. Now define a function to perform the calculation part.

def calculate(userInput):
  return eval(userInput)

NOTE : eval() is an inbuilt method of python which parses the string parameter that i pass into an expression. The string can be a python code or an arithmetic or algebraic expression.

More details on eval method please refer :

https://towardsdatascience.com/python-eval-built-in-function-601f87db191

3. Now that we have the function definition in place, lets pass the user input to the function call.

calculate(userInput)
## or
print(calculate(userInput)) to see the answer.

And that's it you have the calculator functionality set up.

Now lets build a project in QT for making this a GUI application.

This is what we are building today

1. Create a new project on QT designer.

2. Select the option with "Window ( UI file )".

3. Enter project name and path.

4. Enter the class name as below :

5. Click of Finish to end the setup!

6. On the left panel you can see the three files generated [ main.pyproject, form.ui, main.py]

7. Double click on form.ui which opens a drag and drop environment using which u can create input fields and buttons.

8. Follow the below video to setup the button layout :

Now lets convert the form.ui file to a python file

1. Go to the directory where the "form.ui" file is present.

2. Open command prompt in the same directory.

3. Run this command :

pyuic5 form.ui > calculator.py

4. Now "calculator . py " file must be generated in the same directory.

When you open the .py file in a text editor you can see the code.

Now we need to link all the buttons to type particular values in the input field

Lets start with the clear button :

Add this line at the end of "setupUi" method in the auto generated python code

self.pushButton_9.clicked.connect(self.lineEdit.clear)

Note : ( pushButton_9 might be a different button in your case check the labels and then use the push buttons for method calls )

Now let us write two methods at the beginning of the class "Ui_calculator"

def calculate(self,x):
    self.lineEdit.clear()
    def calci():

        self.lineEdit.setText(self.lineEdit.text()+ x)
    return calci
    
def equate(self):
    self.lineEdit.setText(str(eval(self.lineEdit.text())))

Now for the other remaining buttons :

Go back to "setupUi" method and connect them all to "calculate" method :

self.pushButton_16.clicked.connect(self.calculate('1'))

Similarly write for all the other remaining lines.

And that's it!!

Now u can run the .py file and get an output similar to this :

The full code of this project on git : https://github.com/Tejas-Achar/Simple-Calculator

If you want to convert this into a .exe file, follow this post :

https://www.kleverme.com/post/build-an-executable-file-exe-from-a-python-file-py-using-one-simple-command

Peace out!!