How to retrieve a QLabel Value as an Integer

Question

I have written a programme which can control a PWM output on a raspberry pi from the command line but I would now like to control it using a GUI.

I am designing the GUI using PyQt5 to control a PWM output, I would like to retrieve the value from the Label which is adjusted with a dial to then be used to Change the duty cycle of my PWM output.

I am using a raspberry pi 3 Model B+.

I have attached the relevant section of my code below:

Setting up of the Main Window - standard ui to py conversion that happens when using pyuic.

class Ui_MainWindow(object):
def setupUi(self, MainWindow):
    MainWindow.setObjectName("MainWindow")
    MainWindow.resize(800, 600)
    self.centralwidget = QtWidgets.QWidget(MainWindow)
    self.centralwidget.setObjectName("centralwidget")
    self.verticalLayout = QtWidgets.QVBoxLayout(self.centralwidget)
    self.verticalLayout.setObjectName("verticalLayout")
    self.label = QtWidgets.QLabel(self.centralwidget)
    self.label.setAlignment(QtCore.Qt.AlignCenter)
    self.label.setObjectName("label")
    self.verticalLayout.addWidget(self.label)
    self.dial = QtWidgets.QDial(self.centralwidget)
    self.dial.setObjectName("dial")
    self.verticalLayout.addWidget(self.dial)
    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)
    self.dial.valueChanged['int'].connect(self.label.setNum)
    QtCore.QMetaObject.connectSlotsByName(MainWindow)

Function which is trying to retrieve the value from the label and ultimately update the duty cycle.

    def ChangeSpeed(self):
        self.My_PWM.start(0)
        while True:
            if 0 < self.ui.label:
                self.My_PWM.ChangeDutyCycle(self.ui.label)
            elif self.ui.label<0:
                self.My_PWM.ChangeDutyCycle(0)
                print("Programme Ended")
                break

I get a type error: unorderable tyoes int()

This question is not just straight forward conversion as it does not allow be to convert he QLabel Value to an integer.

Thanks!

You have to convert (cast) the text from the label to an `int` first before comparison. See https://stackoverflow.com/questions/14886881/unorderable-types-int-str for more info. — TrebledJ, Nov 13 '18 at 16:39
I have tried that and i get an error which states "int() argument must be a string, a bytes like object or a number, not 'QLabel'". — Almaas Shah, Nov 13 '18 at 16:43
change `self.ui.label` to `int(self.ui.label.text())` in the `ChangeSpeed` method — S. Nick, Nov 13 '18 at 16:44
I literally just tried both of those , but gave me another error. "ValueError invalid literal for int() with base 10: 'TextLabel'" — Almaas Shah, Nov 13 '18 at 16:48
Seems like `self.ui.label.text()` is returning "TextLabel". Then the cast to `int` fails. Maybe provide a check against this? Input validation? — TrebledJ, Nov 13 '18 at 16:52
Possible duplicate of [Short way to convert string to int Python 3](https://stackoverflow.com/questions/41837247/short-way-to-convert-string-to-int-python-3) — eyllanesc, Nov 13 '18 at 16:53
I do not think it is a duplicate, The conventional method of converting a string to an int does not seem to be working hence why i posted this question. — Almaas Shah, Nov 13 '18 at 16:56
@TrebuchetMS it seems as this line which comes after the mainwindow section is affecting is self.label.setText(_translate("MainWindow","TextLabel")) any idea how I can change this? — Almaas Shah, Nov 13 '18 at 17:01

Almaas Shah · Accepted Answer · 2018-11-27T09:04:42.643

Ok to resolve this issue, I had to change the code of the label from "self.label.setText..." to "self.label.setNum(0)", this set the starting value as zero and then standard integer conversion was carried out using int(self.ui.label.text()). I hope this makes sense

The relevant sections of the code were as follows:

  def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setNum(0)
        self.pushButton.setText(_translate("MainWindow", "Set Speed"))

I have since added a push Button To set the duty cycle.

and this was the conversion part of my code:

def ChangeSpeed(self):
        self.My_PWM.start(0)
        if 0 < int(self.ui.label.text()):
            self.My_PWM.ChangeDutyCycle(int(self.ui.label.text()))
        elif int(self.ui.label.text())<0:
            self.My_PWM.ChangeDutyCycle(0)
            print("Programme Ended")

I hope this makes sense for those of you who wish to convert a Qlabel to an int you must be wary that if you use QtDesigner as I did and carry out a pyuic5 conversion it will automatically set any value in your label to a text value or an empty string and you simply have to convert this to a integer using setNum.

How to retrieve a QLabel Value as an Integer

1 Answers1