problems with PyQt5-5.15.0 linux wheel

[Phil Thompson]

On 29/06/2020 04:56, Steve Borho wrote:
>> On Jun 28, 2020, at 2:29 AM, Phil Thompson 
>> <phil at riverbankcomputing.com> wrote:
>> 
>> On 28/06/2020 01:45, Steve Borho wrote:
>>> Hello,
>>> I’ve noticed something unusual about the
>>> PyQt5-5.15.0-5.15.0-cp35.cp36.cp37.cp38-abi3-manylinux2014_x86_64.whl
>>> wheel that is served by PyPi.
>>> If you install it on Ubuntu 20.04 (py3.8) or Ubuntu 18.04(py3.6) it
>>> seems to be ok, but if you install it on Ubuntu 16.04 (py3.5) it does
>>> not install the Qt/plugin/ or Qt/translations/ folder like it does 
>>> for
>>> the other Python versions.
>>> This leads to runtime errors when you try to use PyQt5:
>>> qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even
>>> though it was found.
>>> This application failed to start because no Qt platform plugin could
>>> be initialized. Reinstalling the application may fix this problem.
>>> I checked the PyQt5-5.14.2 wheel on Ubuntu 16.04 (py3.5) and it did
>>> install the plugins and translations, so this looks like a 
>>> regression.
>> 
>> I think Qt v5.15.0 no longer includes its own copy of the xcb 
>> libraries so they have to be installed by the OS.
> 
> I don’t think it is a Qt change, I think it is PyQt related for three 
> reasons:
> 
> 1. On the Python3.5 machines (16.04) we can work around the problem by
> pointing an env var at any local copy of Qt-5.15, so the required
> files are in the Qt distribution.
> 
> QT_QPA_PLATFORM_PLUGIN_PATH=~/Qt/5.15.0/gcc_64/plugins
> 
> 2. If we install the same wheel on a Python3.6 or Python3.7 system, it
> installs these plugins into site-pacakges/PyQt5/Qt/lib/plugins and the
> workaround is unnecessary
> 
> 3. If you manually run sip-install on PyQt-5.15.0 building against
> Qt-5.15.0 with Python3.5, the same thing happens, the plugins are not
> copied into site-pacakges.  But it works fine on Python3.6.

A wheel is just a packaging format - no code is executed when a wheel is 
installed. The same wheel is used for all Python versions. Therefore I'm 
struggling to understand why it would be a problem with the wheel 
itself. I would therefore look at the code that was installing the wheel 
(ie. pip).

Phil