silx.gui.plot: add X inversion action to PlotWindow and ImageToolbar

[loichuder]

Checklist:

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Fix #4253

Screencast.from.2025-09-23.10-43-25.webm

[loichuder]

I completely refactored YAxisOriginToolButton to have a base class to abstract the common behaviour.

The only change between the XAxisOriginToolButton and the YAxisOriginToolButton is the axis to act on (abstracted by getAxis) and the icons/labels (abstracted by getState).

Note that self.STATE was converted to TypedDict, which should be fine given these were introducted in Python 3.8.

Note also that STATE is no longer lazy-loaded. Is this a problem ?

[t20100]

Refactoring sounds good.
The state info is still lazy-loaded, however it's no longer cached.
It shouldn't be an issue: icons are already cached.

[loichuder]

Sorry, went a bit too fast. I still have CI woes to solve.

[t20100]

Looks good!

Main concern is about circular references induced by using lambda: self.method.

[t20100]

This creates a mixed python/qt circular reference (lambda -> self -> menu -> disableInversionAction -> signal -> lambda) which may delay proper deletion, so best to avoid.

WeakMethod can be used here:

Suggested change

	disableInversionAction.triggered.connect(lambda: self.setAxisInverted(False))
	inversionTriggered = WeakMethod(self.setAxisInverted)
	disableInversionAction.triggered.connect(lambda: inversionTriggered(False))

or wrapper methods since signal.connect(self.slot) is handled correctly.

Illustration of the problem:

>>> import weakref
>>> from silx import sx
>>> class A(sx.qt.QObject):
...     def __init__(self):
...         super().__init__()
...         self.objectNameChanged.connect(self.changed)
...     def changed(self, name):
...         print(name)
... 
>>> a = A()
>>> r = weakref.ref(a, lambda ref: print('dead', ref))
>>> del a
dead <weakref at 0x7f48eff53ef0; dead>

>>> class A(sx.qt.QObject):
...     def __init__(self):
...         super().__init__()
...         self.objectNameChanged.connect(lambda n: self.changed(n))
...     def changed(self, name):
...         print(name)
... 
>>> a = A()
>>> r = weakref.ref(a, lambda ref: print('dead', ref))
>>> del a
>>> 
>>> r()
<__main__.A object at 0x7f48fe72eb80>

[loichuder]

In the end, I used wrapper functions (108c45f) instead of weakref.

It seems to have fixed the elusive segfault in the CI !

[t20100]

Good!

IMO we should prevent using lambda functions, functools.partial or anything keeping references to self in signals even if that requires some boilerplate methods.

[loichuder]

Yep. It looks to be recipes for disaster 😞

[t20100]

Refactoring sounds good.
The state info is still lazy-loaded, however it's no longer cached.
It shouldn't be an issue: icons are already cached.

[t20100]

Looks like my suggestions breaks the CI 😅 , I'll have a look

[loichuder]

Looks like my suggestions breaks the CI 😅 , I'll have a look

Missed a renaming from xAxisInvertedAction to _xAxisInvertedAction in PlotWindow. Should be good now 🤞

[loichuder]

Maaan, there is a segfault in the CI that I cannot reproduce locally 😮‍💨