[PyQt] Not understanding instanceof() in this situation
jnbarchan at gmail.com
Wed Aug 15 11:27:02 BST 2018
On 17 July 2018 at 17:38, Kyle Altendorf <sda at fstab.net> wrote:
> I _think_ I see what's going on. You have a file named main.py (you
> probably meant `from main import Main`?) which you run directly such as
> `venv/bin/python main.py`. When you do this it isn't `main` but rather
> `__main__` because you are running it directly and that's what Python does
> in that case. When you import the `main.py` file you get another copy
> imported under the name `main`. Each is separate including unique objects
> being created for the classes defined in `main.py`.
> I almost always use entry_points in my setup.py now instead of running
> files directly. I also make sure to have an installable project any time I
> need to import my own code. Not-installed imports are fiddly... oh, and
> work in a virtualenv (basically required on linux), but i digress.
> On 2018-07-17 08:45, J Barchan wrote:
> Sorry if this turns out to be a general question about Python's
> instanceof() rather than specifically PyQt.....
> For debugging leaks (in a simple fashion) I am walking
> QtWidgets.QApplication.allWidgets() looking at those whose parent() is
> I come across one I wish to ignore. PyCharm debugger shows its class as
> __main__.Main. My code has:
> class Main(QtWidgets.QMainWindow):
> if __name__ == '__main__':
> mainWindow = Main()
> So in my checker I try:
> from main.py import Main
> if isinstance(widget, Main): ...
> But this returns False on the widget. I discovered I can just check
> instead for isinstance(widget, QtWidgets.QMainWindow), so I'm OK and
> that's better anyway.
> But I don't understand why it is not an instance of my Main given that is
> derived from QtWidgets.QMainWindow? Could someone patiently enlighten me?
> PyQt mailing list PyQt at riverbankcomputing.com
Sorry for long delay --- this email went to my *Spam* folder and I never
noticed it till now!
Your analysis is correct.
When you do this it isn't `main` but rather `__main__` because you are
> running it directly and that's what Python does in that case. When you
> import the `main.py` file you get another copy imported under the name
> `main`. Each is separate including unique objects being created for the
> classes defined in `main.py`.
I did not know that. This would affect only my "main" (run from
command-line) module when importing, and it looks pretty disasterous. I
shan't be importing that one again! Thanks :)
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