PyQt5 and Big Sur

Marius Shekow marius.shekow at
Tue Nov 17 13:31:54 GMT 2020

Hi, I also found that setting the environment variable 
QT_MAC_WANTS_LAYER to "1" fixes the problem, as per

No idea, why it works, but it's a good workaround for your early adoper 
users who accuse you, the app developer, to have "broken everything". 
Shame on me... (sarcasm).

Am 15.11.2020 um 23:35 schrieb Jeremy Katz:
> On 15/Nov/20 04:50, Eric Larson wrote:
>> I recently updated to Big Sur (11.0.1). I have Qt5Agg set as my
>> matplotlib backend. Opening a matploltlibĀ figure in interactive mode now
>> causes the interpreter to hang on 5.12 and 5.15.1. Even running a hello
>> world <> example
>> causes the interpreter to hang.
>> I tried the same matplotlib code with pyside2, and there at least the
>> interpreter would not hang. For both PyQt5 and pyside2, however, no
>> window actually showed up, even though an icon did appear. So it seems
>> at least some of this is probably a problem at the level of Qt rather
>> than PyQt5.
> I had an apparent application hang with PyQt and Qt 5.15.0, and an
> application bundle created with PyInstaller. Dtruss revealed that the
> application was executing, but very slowly. IIRC, the main window went
> from displaying in ~5 seconds with macOS Catalina to 4 minutes with Big Sur.
> Running the application once with "open -F" seemed to resolve the issue
> permanently.
Dr. Marius Shekow
Mixed and Augmented Reality Solutions, Fraunhofer FIT
Tel.: +49(0)2241 - 14-3555

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