PyQt5: multiple instances of same window

Question

I\'m having a problem with pyqt5. I have this piece of code to instantiate my class and open my window without closing after the show method (because gc).

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Answer 1

Explanation:

To understand the problem, the following 2 codes and their outputs must be analyzed:

Example1

from PyQt5 import QtCore


if __name__ == "__main__":
    app = QtCore.QCoreApplication([])

    o = QtCore.QObject()
    o.destroyed.connect(lambda: print("destroyed o"))

    o = QtCore.QObject()

    def on_timeout():
        print("quit")
        QtCore.QCoreApplication.quit()

    QtCore.QTimer.singleShot(1000, on_timeout)

    app.exec_()

destroyed o
quit

Example2

from PyQt5 import QtCore


if __name__ == "__main__":
    app = QtCore.QCoreApplication([])

    o = QtCore.QObject()
    o.destroyed.connect(lambda: print("destroyed o"))

    p = o

    o = QtCore.QObject()

    def on_timeout():
        print("quit")
        QtCore.QCoreApplication.quit()

    QtCore.QTimer.singleShot(1000, on_timeout)

    app.exec_()

quit
destroyed o

In the first example, the variable "o" is assigned a QObject and when another QObject is assigned, the initial QObject is deleted, so "destroyed" is printed before "quit".

In the second example, it has the difference "p = o" where reference is made to the QObject, that is, in that line "p" and "o" represent the same object, so by assigning "or" a new QObject the initial QObject is not it destroys, and it is only destroyed when the loop ends and the GC does its job.

That is what happens in your case in a subtle way, the logic of "p = o" is that the QObject is stored in another "place", and in your example that "place" is the lambda that has its own scope ( similarly with partial). Specifically, in your example, a new window was created destroying the previous one, causing a single window to be displayed at all times.

Solution:

One possible solution is to prevent the first window from being removed and a new window created using a flag:

from PyQt5 import QtCore, QtGui, QtWidgets

flag = False

# ...

def open_otherwindow():
    global w, flag
    if not flag:
        w = OtherWindow()
        w.show()
    flag = True

# ...