Using QSignalMapper

Question

I tried to make a simple example to help understand how the concept of QSignalMapping works in PySide. I would like to dynamically create a series of buttons by iterating through a loop, and when the user pushes one of the buttons, I can activate a method that returns the appropriate label for the button that was pressed.

from PySide2 import QtWidgets,QtCore,QtGui

fruit_list = ["apples","oranges","pears"]

def fruit_button_event():
    print "this is the pressed button's label"

def main():
    for fruit in fruit_list:
        fruit_button = QtWidgets.QPushButton(fruit)
        fruit_button.clicked.connect(lambda:fruit_button_event())
main()

Answer 1

In the next part I show an example how to use QSignalMapper:

from PySide2 import QtCore, QtWidgets


class Widget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(Widget, self).__init__(parent)
        lay = QtWidgets.QVBoxLayout(self)

        fruit_list = ["apples","oranges","pears"]
        mapper =  QtCore.QSignalMapper(self)
        mapper.mapped[str].connect(self.fruit_button_event)

        for fruit in fruit_list:
            btn = QtWidgets.QPushButton(fruit)
            btn.clicked.connect(mapper.map)
            mapper.setMapping(btn, fruit)
            lay.addWidget(btn)

    @QtCore.Slot(str)
    def fruit_button_event(self, text):
        print("this is the pressed button's label", text)


if __name__ == '__main__':
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())

Remember that from Qt 5.10 QSignalMapper is deprecated:

This class is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

---

The same functionality in python can be obtained with functools.partial(...):

from PySide2 import QtCore, QtWidgets
from functools import partial


class Widget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(Widget, self).__init__(parent)
        lay = QtWidgets.QVBoxLayout(self)

        fruit_list = ["apples","oranges","pears"]

        for fruit in fruit_list:
            btn = QtWidgets.QPushButton(fruit)
            btn.clicked.connect(partial(self.fruit_button_event, fruit))
            lay.addWidget(btn)

    @QtCore.Slot(str)
    def fruit_button_event(self, text):
        print("this is the pressed button's label", text)

Or with lambda:

btn.clicked.connect(lambda text=fruit: self.fruit_button_event(text))

Or QButtonGroup:

class Widget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(Widget, self).__init__(parent)
        lay = QtWidgets.QVBoxLayout(self)

        fruit_list = ["apples","oranges","pears"]
        group = QtWidgets.QButtonGroup(self)
        group.buttonClicked.connect(self.OnButtonClicked)

        for fruit in fruit_list:
            btn = QtWidgets.QPushButton(fruit)
            group.addButton(btn)
            lay.addWidget(btn)

    @QtCore.Slot(QtWidgets.QAbstractButton)
    def OnButtonClicked(self, btn):
        print("this is the pressed button's label", btn.text())