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Recently I started to learn Python and PyQT5.

So here is my code for a calculator. Personally I don't like how the doMath() function is looking but I don't know how to make it more readable and pythonic.

import operator
import sys
from functools import partial

from PyQt5.QtWidgets import (QApplication, QShortcut, QLabel, QPushButton,
                             QGridLayout, QWidget, QMainWindow, QLineEdit,
                             QVBoxLayout, QLineEdit, QShortcut, QAction)
from PyQt5.QtGui import QKeySequence, QDoubleValidator
from PyQt5.QtCore import QLocale, Qt


class MyWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.setGeometry(0, 0, 200, 300)
        self.setWindowTitle('PyQt5 calculator')
        self.buttonsText = [
            '<-', '=', '+',
            '/', '*', '-',
            '7', '8', '9',
            '4', '5', '6',
            '1', '2', '3',
            'c', '0', '.'
        ]
        self.col_num = 3
        self.operators = {'+': operator.add, '-': operator.sub,
                          '/': operator.truediv, '*': operator.mul}
        self.operand = ''
        self.operator = ''
        self.initUI()
        self.setShortcuts()

    def initUI(self):
        # initialize widgets and layouts
        cenWidget = QWidget(self)
        vertLayout = QVBoxLayout(cenWidget)
        gridWidget = QWidget()
        gridLayout = QGridLayout(gridWidget)
        gridWidget.setLayout(gridLayout)
        self.hintField = QLabel(parent=cenWidget)
        # configure text filed and validator
        self.textField = QLineEdit()
        f = self.textField.font()
        f.setPointSize(18)
        self.textField.setFont(f)
        validator = QDoubleValidator()
        validator.setLocale(QLocale('English'))
        self.textField.setValidator(validator)
        # add widgets to top level layout
        vertLayout.addWidget(self.hintField)
        vertLayout.addWidget(self.textField)
        vertLayout.addWidget(gridWidget)
        # add buttons to grid layout
        self.buttonInstances = [QPushButton(item) for item in self.buttonsText]
        for i, button in enumerate(self.buttonInstances):
            button.clicked.connect(partial(self.doMath, button.text()))
            gridLayout.addWidget(button, i//self.col_num, i % self.col_num)

        self.setCentralWidget(cenWidget)

    def doMath(self, buttonValue):
        currentValue = self.textField.text()
        convertedValue = self.convertValue(currentValue)
        if buttonValue == 'c':
            self.clearFields()
        elif buttonValue == '<-':
            self.textField.setText(currentValue[:-1])
        elif buttonValue == '.':
            if '.' not in currentValue:
                self.textField.setText(currentValue+buttonValue)
        elif (not self.operand and buttonValue in self.operators
              and convertedValue != None):
            self.operator = buttonValue
            self.operand = convertedValue
            self.textField.setText('')
        elif (buttonValue == '=' or buttonValue in self.operators 
              and self.operator and convertedValue):
            answer = self.operators[self.operator](
                     self.operand, convertedValue)
            self.clearFields()
            if buttonValue == '=':
                self.textField.setText(f'{answer}')
            else:
                self.operand = answer
                self.operator = buttonValue
        elif self.convertValue(buttonValue) != None:
            self.textField.setText(currentValue+buttonValue)

        self.hintField.setText(f'<h1><font color=#a0a0a0>{self.operand}' 
                               f'{self.operator}</font></h1>')

    def setShortcuts(self):
        eqShort= QShortcut(QKeySequence('Enter'), self)
        eqShort.activated.connect(partial(self.doMath, '='))
        for sign in self.buttonsText[1:5]:
            short= QShortcut(QKeySequence(sign), self)
            short.activated.connect(partial(self.doMath, sign))


    def convertValue(self, value):
        try:
            return int(value)
        except ValueError:
            try:
                return float(value)
            except:
                return None

    def clearFields(self):
        self.operand = ''
        self.operator = ''
        self.textField.setText('')

app = QApplication(sys.argv)
window = MyWindow()
window.show()
sys.exit(app.exec_())
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Make use of this small project to separate core logic from UI. You can have a class Calculator which retains current state, and your UI is just a way to display this class.

To do this, just think your design as if you were to replace UI by CLI. You have to be able to unplug your UI, plug CLI, and your calculator has to work the same. This is also, I think, an easier way to write unit tests or run batch functional tests.

It mainly concerns doMath and convertValue, which has nothing to do in UI code. Actually convertValue might disappear even in a Calculator class, because you will have the real value stored.

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