Ability to override method on object instance

[ktprograms]

Is your feature request related to a problem? Please describe. The project I am working on uses PyQt for its GUI. I want to make acceptsFirstMouse_ return False (it currently doesn't deep inside PyQt platform-specific code). Due to the architecture, I can't figure out how the "normal" way of subclassing NSView would work since the view is already initialized by PyQt, so I'm trying to set a function for the acceptsFirstMouse_ instance "variable".

Here's the code I'm using:

def acceptsFirstMouse_(self, event):
    return False

from objc import objc_object
from AppKit import NSView
view = objc_object(c_void_p=c_void_p(int(self.winId())))
view.acceptsFirstMouse_ = acceptsFirstMouse_.__get__(view, NSView)

I'm getting this error when running:

AttributeError: 'QNSView' object attribute 'acceptsFirstMouse_' is read-only

Describe the solution you'd like Ability to override methods in this way without subclassing.

Describe alternatives you've considered I can't think of any. Is it possible to use a subclass of NSView somehow with PyQt (I'd like the whole window to have acceptsFirstMouse_ as False).

[ronaldoussoren]

It is not possible to implement this. The method (acceptsFirstMouse:) is called in Objective-C, with method resolution in the Objective-C runtime. That method resolution only looks at methods in the class and does not know about (Python) instance attributes.

In theory it could be possible to implement a hack for this, but that would affect all instances of the class and would be fragile at best. I won't implement this.

In your case Qt's WindowTransparentForInput flag might help, although that affects both mouse and keyboard input.

In general it is possible to override a method on the class using something like the code below, although that likely won't work in your case:

QNSView = objc.lookUpClass("QNSView")

# Store a reference to the current method implementation:
orig_imp = QNSView. instanceMethodForSelector_(b"acceptsFirstMouse:")

# New implementation:
def acceptsFirstMouse_(self, event):
     if hasattr(self, "overrideAcceptsFirstMouse_"):
         return self.overrideAcceptsFirstMouse_(event)

     # Fall back to the original implementation
     return orig_imp(self, event)

# Replace method on the class:
QNSView. acceptsFirstMouse_ = acceptsFirstMouse_

This doesn't work because instances of QNSView should not have a __dict__ attribute, meaning it is not possible to add the overrideAcceptsFirstMouse_ attribute. Adding a __dict__ for arbitrary Objective-C objects is not possible, this would require adding instance attributes to the Objective-C class to do this reliably.

The pattern could work if you have some other way to check if self is a widget for which you want to override the return value.

[ktprograms]

Thanks for the detailed explanation.

I'll just have to wait then, as according to this it looks like it'll be possible in QT 6.5.