I don't understand the condition in the following code:
self.destroyed.connect(lambda: ViewBox.forgetView(sid, name) if (ViewBox is not None and 'sid' in locals() and 'name' in locals()) else None)
from https://github.com/pyqtgraph/pyqtgraph/blob/master/pyqtgraph/graphicsItems/ViewBox/ViewBox.py#L284-L288
and explicitly added in e5f383f

Based on my testing script below, the expression 'sid' in locals() and 'name' in locals() is always True, since they are referenced in the expression ViewBox.forgetView(sid, name)

def func_indirect(x):
    return x

def func1(x):
    # "'x' in locals" is True 
    return lambda : func_indirect(x) if 'x' in locals() else None

def func2(x):
    y = 2 * x
    # "'y' in locals" is False
    return lambda : func_indirect(x) if 'y' in locals() else None

print(func1(1)())   # 1
print(func2(2)())   # None

I got interested in what was happening with locals() in the lambda. I agree, looks like it must always be true. I wondered if there had been a change in python since that was written, but see the same output for your test in python 2.7 and 3.2.

While trying to fix interactive.py to not trigger warnings on PySide 6.7, I am not sure if I have stumbled onto a bug. The 3rd commit in this PR does a check for connections before attempting to disconnect; and this does manage to prevent some of the warnings.

However, despite this check, there are still 2 failures to disconnect of sigValueChanged.
These failures are actually present in all bindings.
i.e. previously, these real failures were just being ignored

UPDATE: So there isn't any bug. The issue with my failed attempt is that knowing that a signal has slot(s) connected is not a sufficient condition for ascertaining whether a particular slot is connected.
For this case, sigValueChanged is already connected elsewhere which makes the receivers() count always positive.

Thanks @pijyoi Always nice when we can address an issue before the upstream library makes a change. Appreciate your effort to look ahead and mitigate issues per-emptively.

I don't understand the condition in the following code: self.destroyed.connect(lambda: ViewBox.forgetView(sid, name) if (ViewBox is not None and 'sid' in locals() and 'name' in locals()) else None) from https://github.com/pyqtgraph/pyqtgraph/blob/master/pyqtgraph/graphicsItems/ViewBox/ViewBox.py#L284-L288 and explicitly added in e5f383f

Based on my testing script below, the expression 'sid' in locals() and 'name' in locals() is always True, since they are referenced in the expression ViewBox.forgetView(sid, name)

Sorry for the late reply @pijyoi ! The reason for this code is that the callback can be invoked during python teardown (in which case some of these locals may already have been deleted). I think this just avoids error messages that would appear on exit, but it's also possible that it prevented segmentation faults at exit, which were common at the time this was written.