Plugin devs: Upcoming migration to Qt 6

[kovidgoyal]

@jackie_w: Thanks, fixed by: https://github.com/kovidgoyal/calibr...3d57adaa187c3c

[kovidgoyal]

Released version 5.99.1 with fixes for all issues reported so far (other than thiago's checkbox shadows)

[thiago.eec]

Originally Posted by kovidgoyal

Released version 5.99.1 with fixes for all issues reported so far (other than thiago's checkbox shadows)

My issues are caused by Qt's new High DPI Scaling policy. It only affects those using a non-integer scale factor. In my case, I use 125%. This is a known issue of Qt6, as pointed here.

This causes some graphical glitches. In my case:

- Kind of a shadow on some checkboxes
- Missing separators
- Small icons are drawed with poor quality (the same ones that looked ok on Qt5).
- The whole calibre interface got "bigger". I have bigger icons, bigger line spaces, etc.

For the icons on my plugins, I just used larger ones, but the rest of the problems remained. So, I dealed with it by setting this environment variable:

QT_ENABLE_HIGHDPI_SCALING = 0

This is the standard look. Bigger interface, missing separators on plugin menu.


After setting the environment variable.

[dunhill]

Excellent. Is the beta? in the beta section?

[davidfor]

@DNSB reported to me an error on some of the plugins I look after. The error was:

ModuleNotFoundError: No module named 'PyQt4'

Which is being triggered by one of the imports from the Qt5 not loading and attempts to load Qt4 happen.

When I looked the original error was:

Traceback (most recent call last):
  File "calibre_plugins.goodreads.config", line 16, in <module>
ImportError: cannot import name 'Qt' from 'qt' (E:\CalibrePortable599\Calibre Portable\Calibre\app\bin\python-lib.bypy.frozen\qt\__init__.pyc)

Which comes from the line:

    from PyQt5 import Qt as QtGui

Is this something missed or do we need to change this? Looking through the code, "QtGui" is used mainly for some enums/type but, also a few classes that were not explicitly imported.

[jhowell]

Originally Posted by kovidgoyal

@jackie_w You need to use fully qualified names for enums in PyQt6, as thiago pointed out. I have added compatibility layers for the most common enums in calibre so they can continue to be used as before, but not for all of them.

One I use that no longer works in the beta is QTextEdit.NoWrap.

Should I change this to QTextEdit.LineWrapMode.NoWrap or will you add that to the compatibility layer?

If I change it to the fully qualified enum will it be backward compatible with older versions of calibre?

[kovidgoyal]

@davidfor: The PyQt5.Qt module was a shortcut module for importing other Qt classes from a common namespace that was removed in PyQt6. It should not be used and and definitely not aliased as QtGui which is a different module altogether.

Indeed, from calibre 5.13 onwards you can simply do all Qt related imports as

from qt.core import whatever

It works on qt 5 and qt 6. This is what is used in calibre source code itself.

@jhowell: Yes, QTextEdit is rather too specialised for me too add a compat layer for it. Ans yes, the fully qualified names work with calibre 5.x as well. Not sure about even earlier versions though.

[kovidgoyal]

Originally Posted by dunhill

Excellent. Is the beta? in the beta section?

The link to the betas is in the first post of this thread.

[davidfor]

Originally Posted by kovidgoyal

@davidfor: The PyQt5.Qt module was a shortcut module for importing other Qt classes from a common namespace that was removed in PyQt6. It should not be used and and definitely not aliased as QtGui which is a different module altogether.

Indeed, from calibre 5.13 onwards you can simply do all Qt related imports as

from qt.core import whatever

It works on qt 5 and qt 6. This is what is used in calibre source code itself.

The example I was looking at was the Goodreads Metadata source plugin. Which was one of @kiwidudes. The code for importing Qt is:

try:
    from PyQt5 import Qt as QtGui
    from PyQt5.Qt import (QTableWidgetItem, QVBoxLayout, Qt, QGroupBox, QTableWidget,
                          QCheckBox, QAbstractItemView, QHBoxLayout, QIcon,
                          QInputDialog)
except ImportError:
    from PyQt4 import QtGui
    from PyQt4.Qt import (QTableWidgetItem, QVBoxLayout, Qt, QGroupBox, QTableWidget,
                          QCheckBox, QAbstractItemView, QHBoxLayout, QIcon,
                          QInputDialog)

And then used like:

        spacerItem1 = QtGui.QSpacerItem(20, 40, QtGui.QSizePolicy.Minimum, QtGui.QSizePolicy.Expanding)
        button_layout.addItem(spacerItem1)
        remove_mapping_button = QtGui.QToolButton(self)

And that's pretty common in the plugins. I assume the first line was a cheat so that we didn't have to change the code that was using QtGui from Qt4. I'll have a look to see how easy it is to change, but, it might be time to drop the Qt4 support.

[kovidgoyal]

Yes, its definitely time to drop Qt4 support. Though if you dont want to, you could in theory do this:

try:
    import qt.core as QtGui
except ImportError:
    try:
        from PyQt5 import Qt as QtGui
    except ImportError:
        from PyQt4 import QtGui

[davidfor]

Originally Posted by thiago.eec

Not tested, but a suggestion based on the problems I found porting my plugins... maybe you should use:

QTableWidgetItem.ItemType.UserType

https://doc.qt.io/qt-6/qtablewidgeti...#ItemType-enum

That didn't work here. I had to use:

QTableWidgetItem.ItemType.UserType.value

And that doesn't work with Qt5. I get:

AttributeError: 'ItemType' object has no attribute 'value'

for the lines that use the above.

And with out the ".value", with Qt6, the error is:

TypeError: QTableWidgetItem(): arguments did not match any overloaded call:
  overload 1: argument 1 has unexpected type 'str'
  overload 2: argument 2 has unexpected type 'ItemType'
  overload 3: argument 1 has unexpected type 'str'
  overload 4: argument 1 has unexpected type 'str'

The line is:

super(ReadOnlyTableWidgetItem, self).__init__(text, QTableWidgetItem.ItemType.UserType)

With the ".value" for the Qt6 version.

What have I missed?

[rcentros]

Originally Posted by kovidgoyal

calibre comes with its own copy of Qt, it doesn't care what Qt is on the host system. You do however need a recent enough version of glibc, which for calibre 6 is IIRC 2.31 which will be about two years old at the time of calibre 6 release.

Originally Posted by Moonbase59

Thanks! Yes, my glibc is 2.31 (Linux Mint 20.2).

It looks like I'll be using Calibre 5.x through April, 2023 when my Linux Mint 19.3 goes to EOL. 19.3 is still at glib 2.27. I just recently upgraded from 4.x to 5.x because I wanted to use a specific plugin (DeASCM). I don't mind being on the trailing edge.

[kovidgoyal]

@davidfor: That's a bug in PyQt6. Just use the literal 1000 it should work in both. Or if you want to be elegant:

try:
    MyType = QTableWidgetItem.ItemType.UserType.value
except AttributeError:
    MyType = QTableWidgetItem.UserType

Sadly, Phil decided to move PyQt to using python enums in PyQt6 and caused endless bugs and breakage in the process. There are literally hundreds of commits I've had to make to fix all the breakage this decision has caused.

[davidfor]

Originally Posted by kovidgoyal

@davidfor: That's a bug in PyQt6. Just use the literal 1000 it should work in both. Or if you want to be elegant:

try:
    MyType = QTableWidgetItem.ItemType.UserType.value
except AttributeError:
    MyType = QTableWidgetItem.UserType

Sadly, Phil decided to move PyQt to using python enums in PyQt6 and caused endless bugs and breakage in the process. There are literally hundreds of commits I've had to make to fix all the breakage this decision has caused.

I was afraid of that. And that is a bad decision. It defeats the purpose of the types if you can't just use them.

[jackie_w]

Originally Posted by kovidgoyal

@davidfor: That's a bug in PyQt6. Just use the literal 1000 it should work in both. Or if you want to be elegant:

try:
    MyType = QTableWidgetItem.ItemType.UserType.value
except AttributeError:
    MyType = QTableWidgetItem.UserType

I'd already realised that this works:

QTableWidgetItem.__init__(self, text, 1000)

but thanks for the elegant option which also works.

I'm fairly sure the code both @davidfor and myself are using originates from @kiwidude's early plugins. Sorry if this is a dumb question, is there a good reason why a UserType needs to be specified at all, because this also appears to work? Presumably it defaults to a UserType of zero:

QTableWidgetItem.__init__(self, text)