why is there no reference between the app and the widget?

问题

This is a follow up to why will the application show after sys.exit command?

I'm following this tutorial:

http://zetcode.com/tutorials/pyqt4/firstprograms/

I modified the code slightly to test things

import sys
from PyQt4 import QtGui


if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    w = QtGui.QWidget()
    w.resize(250,150)
    w.move(300,300)
    w.setWindowTitle("Title")
    w.show()
    sys.exit(app.exec_())

I'm confused as to why there isn't a reference of app and w i'd expect some kind of indication that w is a child or something of app.

I'm running it in Spyder and an IPython interpreter.

回答1:

For any GUI application using Qt, there is precisely one QApplication object, no matter whether the application has 0, 1, 2 or more windows at any given time. All windows are automatically managed by the Application.

You do have to initialize it and to get a hold of it to exec it though.

You must create the Application before any other GUI objects (because they are managed by it).

Detailed Description of the QApplication object

来源：https://stackoverflow.com/questions/15689313/why-is-there-no-reference-between-the-app-and-the-widget

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python