How can I share data with a pyside2 slot function?

I have a PySide2 GUI application with a QPushButton button with a @Slot function connected to it. How can I share data with the function?

from PySide2.QtCore import Slot
from PySide2.QtWidgets import QApplication, QMainWindow, QWidget, QPushButton, QVBoxLayout

@Slot()
def button_XYZ_callback():
    # Function which is executed when the button XYZ is clicked.
    # I'd like to access the __main__s context data "parent_data" here.
    pass

if __name__ == '__main__':
    # parent context data what I want to access (read only)
    parent_data = "blub"

    application = QApplication(sys.argv)
    window = QMainWindow()
    central_widget = QWidget()
    xyz_button = QPushButton("XYZ", central_widget)
    xyz_button.clicked.connect(button_xyz_callback)
    layout = QVBoxLayout(central_widget)
    layout.addWidget(xyz_button)
    window.show()
    sys.exit(application.exec_())

Solution

Per Python's LEGB rule, the global variable parent_data is accessible from within the button_XYZ_callback function.

If, however, you wish to reduce the function's dependence on global variables, the standard technique is to define a class, and use class or instance attributes to store what was before global values:

# based on code from https://wiki.qt.io/Qt_for_Python_Tutorial_ClickableButton
import sys
from PySide2 import QtCore, QtWidgets, QtGui


class MyWidget(QtWidgets.QWidget):
    def __init__(self, data):

        QtWidgets.QWidget.__init__(self)
        self.data = data
        self.button = QtWidgets.QPushButton("Click me!")
        self.text = QtWidgets.QLabel("Hello World")
        self.text.setAlignment(QtCore.Qt.AlignCenter)
        self.layout = QtWidgets.QVBoxLayout()
        self.layout.addWidget(self.text)
        self.layout.addWidget(self.button)
        self.setLayout(self.layout)
        self.button.clicked.connect(self.button_XYZ_callback)

    @QtCore.Slot()
    def button_XYZ_callback(self):
        print(self.data)

if __name__ == "__main__":
    parent_data = "blub"
    app = QtWidgets.QApplication(sys.argv)
    widget = MyWidget(data=parent_data)
    widget.show()
    sys.exit(app.exec_())

Alternatively, if the data is known before the callback is to be defined, you could use a function factory to place the data in the enclosing scope of the callback:

import sys
from PySide2.QtCore import Slot
from PySide2.QtWidgets import QApplication, QPushButton


def make_callback(data):
    @Slot()
    def button_XYZ_callback():
        print(data)
    return button_XYZ_callback

if __name__ == "__main__":
    parent_data = "blub"
    # https://wiki.qt.io/Qt_for_Python_Tutorial_ClickableButton
    app = QApplication(sys.argv)
    button = QPushButton("Click me")
    button.clicked.connect(make_callback(parent_data))
    button.show()
    app.exec_()