calculator.py

import sys
from PyQt5.QtWidgets import QApplication
from PyQt5.QtWidgets import QLabel
from PyQt5.QtWidgets import QWidget
from PyQt5.QtWidgets import QMainWindow
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QGridLayout
from PyQt5.QtWidgets import QVBoxLayout
from PyQt5.QtWidgets import QLineEdit
from PyQt5.QtWidgets import QPushButton
from functools import partial

__version__ = "0.1"
ERROR_MSG = "ERROR"
class calcgui(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("calc")
        self.setFixedSize(300,300)
        self.generalLayout = QVBoxLayout()
        self._centralWidget = QWidget(self)
        self.setCentralWidget(self._centralWidget)
        self._centralWidget.setLayout(self.generalLayout)
        self._createDisplay()
        self._createButtons()
    def _createDisplay(self):
            self.display = QLineEdit()
            self.display.setFixedHeight(50)
            self.display.setAlignment(Qt.AlignLeft)
            self.display.setReadOnly(True)
            self.generalLayout.addWidget(self.display)
    def _createButtons(self):
        self.buttons = {}
        buttonsLayout = QGridLayout()
        buttons = {"7":(0,0),
                    "8":(0,1),
                    "9":(0,2),
                    "C":(0,3),
                    "/":(0,4),
                    "4":(1,0),
                    "5":(1,1),
                    "6":(1,2),
                    "*":(1,3),
                    "(":(1,4),
                    "1":(2,0),
                    "2":(2,1),
                    "3":(2,2),
                    "-":(2,3),
                    ")":(2,4),
                    "0":(3,0),
                    "00":(3,1),
                    ".":(3,2),
                    "+":(3,3),
                    "=":(3,4)
            }
        for btnText, pos in buttons.items():
                self.buttons[btnText] = QPushButton(btnText)
                self.buttons[btnText].setFixedSize(50,50)
                buttonsLayout.addWidget(self.buttons[btnText],pos[0],pos[1])

        self.generalLayout.addLayout(buttonsLayout)

    def setDisplayText(self, text):
        self.display.setText(text)
        self.display.setFocus()

    def DisplayText(self):
        return self.display.text()
    def clearDisplay(self):
        self.setDisplayText("")
class pycalcu:
    def __init__(self,model,view):
        self._evaluate = model
        self._view = view
        self._connectSignals()
    def _calculateResult(self):
        result = self._evaluate(expression=self._view.DisplayText())
        self._view.setDisplayText(result)
    def _buildExpression(self,sub_exp):
        if self._view.DisplayText() == ERROR_MSG:
            self._view.clearDisplay()
        expression = self._view.DisplayText() + sub_exp
        self._view.setDisplayText(expression)
    def _connectSignals(self):
        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.buttons["C"].clicked.connect(self._view.clearDisplay)
        return self._view.display.returnPressed.connect(self._calculateResult)

def evaluateExpression(expression):
    try:
        result = str(eval(expression, {}, {}))
    except Exception:
        result = ERROR_MSG
    return result


def main():
    pycalc = QApplication(sys.argv)
    view = calcgui()
    view.show()
    model = evaluateExpression
    pycalcu(model=model,view=view)
    sys.exit(pycalc.exec_())
if __name__ == "__main__":
    main()