How to compute a value without clicking a button in pyqt5? - pyqt5

Question

How can I compute the net price (Price * (1 - discount)) automatically whenever I enter data? I can make it work on a button press but I'd like to do it whenever data is entered.
See image below.
Thank you in advance!

Answer 1

At first it seems like you are using QLineEdit for the input. Because you want to input integers, I would recommend using the QSpinBox or QDoubleSpinBox, which are made for the input of integers.
I built up such a GUI like you have with QtCreator and converted it with pyuic5 -x gui.ui -o gui.py on my Raspberry Pi to Python.
You simply need to connect the value change of the SpinBox with a function that gives out the net price. For doing this, see the code below:
# -*- coding: utf-8 -*-
from PyQt5 import QtCore, QtGui, QtWidgets
class Ui_MainWindow(object):
def setupUi(self, MainWindow):
MainWindow.setObjectName("MainWindow")
MainWindow.resize(800, 415)
self.centralwidget = QtWidgets.QWidget(MainWindow)
self.centralwidget.setObjectName("centralwidget")
self.label = QtWidgets.QLabel(self.centralwidget)
self.label.setGeometry(QtCore.QRect(30, 40, 201, 81))
font = QtGui.QFont()
font.setPointSize(26)
self.label.setFont(font)
self.label.setObjectName("label")
self.label_2 = QtWidgets.QLabel(self.centralwidget)
self.label_2.setGeometry(QtCore.QRect(30, 140, 201, 81))
font = QtGui.QFont()
font.setPointSize(26)
self.label_2.setFont(font)
self.label_2.setObjectName("label_2")
self.label_3 = QtWidgets.QLabel(self.centralwidget)
self.label_3.setGeometry(QtCore.QRect(30, 260, 201, 81))
font = QtGui.QFont()
font.setPointSize(26)
self.label_3.setFont(font)
self.label_3.setObjectName("label_3")
self.label_netprice = QtWidgets.QLabel(self.centralwidget)
self.label_netprice.setGeometry(QtCore.QRect(260, 282, 421, 41))
self.label_netprice.setStyleSheet("background-color: rgb(255, 255, 255);")
self.label_netprice.setText("")
self.label_netprice.setObjectName("label_netprice")
self.doubleSpinBox_price = QtWidgets.QDoubleSpinBox(self.centralwidget)
self.doubleSpinBox_price.setGeometry(QtCore.QRect(260, 60, 421, 41))
self.doubleSpinBox_price.setObjectName("doubleSpinBox_price")
####################################
# Link to function when value changes
self.doubleSpinBox_price.valueChanged.connect(self.Refresh)
####################################
self.doubleSpinBox_discount = QtWidgets.QDoubleSpinBox(self.centralwidget)
self.doubleSpinBox_discount.setGeometry(QtCore.QRect(260, 160, 421, 41))
self.doubleSpinBox_discount.setObjectName("doubleSpinBox_discount")
####################################
# Link to function when value changes
self.doubleSpinBox_discount.valueChanged.connect(self.Refresh)
####################################
MainWindow.setCentralWidget(self.centralwidget)
self.menubar = QtWidgets.QMenuBar(MainWindow)
self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
self.menubar.setObjectName("menubar")
MainWindow.setMenuBar(self.menubar)
self.statusbar = QtWidgets.QStatusBar(MainWindow)
self.statusbar.setObjectName("statusbar")
MainWindow.setStatusBar(self.statusbar)
self.retranslateUi(MainWindow)
QtCore.QMetaObject.connectSlotsByName(MainWindow)
def retranslateUi(self, MainWindow):
_translate = QtCore.QCoreApplication.translate
MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
self.label.setText(_translate("MainWindow", "Price:"))
self.label_2.setText(_translate("MainWindow", "Discount:"))
self.label_3.setText(_translate("MainWindow", "Net Price:"))
##########################################
# Function for refreshing the output label
def Refresh(self):
price = self.doubleSpinBox_price.value()
discount = self.doubleSpinBox_discount.value()
netprice = price * (1 - discount)
self.label_netprice.setText(str(netprice))
##########################################
if __name__ == "__main__":
import sys
app = QtWidgets.QApplication(sys.argv)
MainWindow = QtWidgets.QMainWindow()
ui = Ui_MainWindow()
ui.setupUi(MainWindow)
MainWindow.show()
sys.exit(app.exec_())
In my code the SpinBoxes are limited at 99 but you can set this to a higher value.
Just a hint: People are more likely to help you, if you give them a short but relatable code example to work with and they don't have to build their own GUI.
I hope this helps. If you find it useful, please mark it as correct.
Best wishes,
RaspiManu