Basic Calculator using Python PyQt

This app is divided in three main parts as per MCV.

1: Create View:

View is basically GUI of an application. In this calc it is grid of numbers and symbols.

2: Create Controller

It is a class that connects interactions between model and view

3: Create Model

This is business logic. In this calc it is just calculations of operations such as addition and multiplication.

Steps

1: Install pyqt

2: Test installation

To check installation and basic woking of pyqt follow steps below

• Create file test.py

import sys

from PyQt5.QtWidgets import QAplication
from PyQt5.QtWidgets import QLabel
from PyQt5.QtWidgets import QWidget

• Go to CMD and run python test.py If installtion is working this run will not give any error

• Now add following lines to check how to create GUI in pyqt

This code is going to create GUI but will not retain window(When you run code it will show window and exit)

app = QApplication(sys.argv)

window = QWidget()
window.QLabel("This is Test", parent = window)
window.show()

• To retain window add following code

sys.exit(app.exce_())

• Also, add following code lines to experiment moe

window.setGeometry(100, 100, 280, 80) # It will set  x, y, w, h of app window
window.move(600,400) # Move window x from left and y from top

3: Create view of application i.e. GUI

• Create class named view.py
• Import following modules

from PyQt5.QtWidgets import QMainWindow
from PyQt5.QtWidgets import QWidget
from PyQt5.QtWidgets import QGridLayout
from PyQt5.QtWidgets import QLineEdit
from PyQt5.QtWidgets import QPushButton
from PyQt5.QtWidgets import QVBoxLayout

• Create class GUI with parent set to QMainWindow

class GUI(QMainWindow):

• Add Constructor ...It will initiate main window by calling superclass constuctor and setting basic parametes such as ..* WindowTitle ..* Size ..* generalLayout ..* LED Display ..* Buttons

• Define methods ..* _createDisplayLED ..* _createButtons ..* setDisplayText ..* getDisplayText ..* clearDisplay

4: Create Model of application

• Evaluting the Expression

def evaluateExpression(expression):
    """Evaluate an expression."""
    try:
        result = str(eval(expression, {}, {})) 
    except Exception:
        result = ERROR_MSG

    return result

5: Create Controller of application

• Create a Controller class to connect the GUI and the model Evaluate expressions.

result = self._evaluate(expression=self._view.getDisplayText())
        self._view.setDisplayText(result)

Build expression.

if self._view.getDisplayText() == ERROR_MSG:
            self._view.clearDisplay()
expression = self._view.getDisplayText() + sub_exp
self._view.setDisplayText(expression)

Connect signals and slots.

for btnText, btn in self._view.buttons.items():
            if btnText not in {'=', 'C'}:
                btn.clicked.connect(partial(self._buildExpression, btnText))

self._view.buttons['='].clicked.connect(self._calculateResult)
self._view.display.returnPressed.connect(self._calculateResult)
self._view.buttons['C'].clicked.connect(self._view.clearDisplay)