Send additional variable during PyQt PushButton click

Question

I'm new to Python and PyQt and this is my first application. Currently when a button is clicked, toggleLED() checks self.LedOn to decide whether to turn an LED on.

class Screen(QWidget):

    def initUI(self):
        self.LedOn = 0

        btn = QPushButton('Off', self)
        btn.setCheckable(True)
        btn.clicked.connect(self.toggleLED)


    def toggleLED(self, pressed):

        source = self.sender()

        if self.LedOn:
            source.setText('Off')
            source.LedOn = 0
            self.serial.write('L')
        else:           
            source.setText('On')
            source.LedOn = 1
            self.serial.write('H')

Problem: Now if we want to control multiple LEDs and remember their individual toggle state, what is the best practice?

I also cant seem to pass an additional value to toggleLED() with btn.clicked.connect(self.toggleLED(btnNumber))

class Screen(QWidget):

    def initUI(self):

        btn1 = QPushButton('Off', self)
        btn1.setCheckable(True)
        btn1.LedOn= 0
        btn1.clicked.connect(selftoggleLED(1))

        btn2 = QPushButton('Off', self)
        btn2.setCheckable(True)
        btn2.LedOn= 0
        btn2.clicked.connect(selftoggleLED(2))


    def toggleLED(self, pressed, value):

        source = self.sender()

        if self.LedOn:
            source.setText('Off')
            self.serial.write(value)
            self.serial.write('L')
        else:           
            source.setText('On')
            self.serial.write(value)
            self.serial.write('H')

I believe you need to subclass QPushButton and somehow reimplement clicked or pressed signal emmiters to return your desired value, but I can't find how to do this in pyqt's documentation — Mario Gil, Dec 09 '16 at 11:14

score 7 · Answer 1 · edited Sep 24 '14 at 14:20

7

You can use partial for that:

from functools import partial

btn1.clicked.connect(partial(self.toggleLED, 1))

This allows you to pass multiple arguments to a function.

edited Sep 24 '14 at 14:20

Stefan van den Akker

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answered Sep 20 '13 at 23:37

Achayan

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score 3 · Answer 2 · answered Oct 03 '14 at 18:20

3

To pass multiple arguments to a function, you can use either functools.partial() or a lambda:

btn2.clicked.connect(lambda: selftoggleLED(2))

Read the discussion of both methods.

answered Oct 03 '14 at 18:20

Stefan van den Akker

6,661
7
48
63

qurban · Answer 3 · 2013-09-29T10:55:41.677

Here is the solution that I always use for this job.

class Screen(QWidget):

    def initUI(self):

        btn1 = QPushButton('Off', self)
        btn1.setCheckable(True)
        btn1.LedOn= 0
        btn1.clicked.connect(selftoggleLED(1))

        btn2 = QPushButton('Off', self)
        btn2.setCheckable(True)
        btn2.LedOn= 0

        # I am adding these lines-----------------------

        # put all the btns in a list
        btns = [btn1, btn2]
        # connect each btn with the function and pass the same btn
        map(lambda btn: btn.clicked.connect(lambda pressed: self.toggleLED(pressed, btn)), btns)


    def toggleLED(self, pressed, clikedBtn):

        if pressed:
            clickedBtn.setText("On")
            # set other variables you need
        else: 
            clickedBtn.setText("Off")
            # set other variables

fasked · Answer 4 · 2013-09-23T03:31:24.923

QPushButton does already have checked boolean property, so you don't need to create another one. There are two signals which button emits:

clicked when it's pressed
toggled when its state is changed

Both of them transfer parameter which indicates a button's state. But I think, the second is more appropriate because of its name.

So the toggleLED slot should looks like this:

def toggleLED(self, checked):
    source = self.sender()
    if checked:
        source.setText('Off')
        self.serial.write('L')
    else:           
        source.setText('On')
        self.serial.write('H')

Notice that only checkable buttons emit toggled signal, but you already set this property in your code:

def initUI(self):
    btn1 = QPushButton('Off', self)
    btn1.setCheckable(True)
    btn1.toggled.connect(self.toggleLED)

    btn2 = QPushButton('Off', self)
    btn2.setCheckable(True)
    btn2.toggled.connect(self.toggleLED)

score 0 · Answer 5 · answered Sep 23 '13 at 02:34

class Screen(QWidget):

    def initUI(self):

        btn1 = QPushButton('Off', self)
        btn1.setCheckable(True)
        btn1.value = 1
        btn1.clicked.connect(selftoggleLED)

        btn2 = QPushButton('Off', self)
        btn2.setCheckable(True)
        btn2.value = 2
        btn2.clicked.connect(selftoggleLED)


    def toggleLED(self, pressed):

        source = self.sender()

        if pressed:
            source.setText('Off')
            self.serial.write(source.value)
            self.serial.write('L')
        else:           
            source.setText('On')
            self.serial.write(source.value)
            self.serial.write('H')

The checkable QPushButton will store the state, so you don't need btn.LedOn.
Use btn.value to store the btn number, so you don't need to send the extra arg.

Send additional variable during PyQt PushButton click

5 Answers5

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