Add __repr__ for QColor?

[RoadrunnerWMC]

Sorry for double-emailing, but I just remembered that PyQt already has at
least one example of a repr that switches constructors depending on the
object's values:

>>> QtCore.QPoint(0, 0)
> PyQt6.QtCore.QPoint()
> >>> QtCore.QPoint(0, 1)
> PyQt6.QtCore.QPoint(0, 1)


So it wouldn't be too crazy to do something similar for QColor too, in my
opinion.

On Tue, Apr 4, 2023 at 9:17 PM RoadrunnerWMC <roadrunnerwmc at gmail.com>
wrote:

> For what it's worth, I'd also like this. The core geometry classes
> (QPoint, QRect, QLine, etc. and their float versions) have custom reprs,
> and I've definitely been bitten by wrongly assuming that QColor has one
> when debugging in the past.
>
> That said, it should use the same syntax as those other classes, instead
> of what QGIS's monkeypatch does:
>
> >>> from PyQt6 import QtCore, QtGui, QtWidgets
>> >>> app = QtWidgets.QApplication([])
>> >>>
>> >>> QtCore.QPoint(1, 2)
>> PyQt6.QtCore.QPoint(1, 2)
>> >>> QtCore.QRectF(1, 2, 3, 4)
>> PyQt6.QtCore.QRectF(1.0, 2.0, 3.0, 4.0)
>> >>>
>> >>> QtGui.QColor(1, 2, 3, 4)
>
> <PyQt6.QtGui.QColor object at 0x7fad4120b840>
>
> >>>
>
> >>> # Showing *hypothetical* new QColor reprs from here on.
>
> >>>
>
> >>> QtGui.QColor(1, 2, 3, 4)
>> PyQt6.QtGui.QColor(1, 2, 3, 4)
>> >>> # since alpha defaults to 255, perhaps it could be omitted if it has
>> that value:
>> >>> QtGui.QColor(1, 2, 3, 255)
>> PyQt6.QtGui.QColor(1, 2, 3)
>
>
> Returning "a string that would yield an object with the same value when
> passed to eval()" is good style
> <https://docs.python.org/3/library/functions.html#repr>, so this output
> format makes sense.
>
> There's a problem, though: showing the components as 8-bit integers would
> be misleading, since QColor uses higher precision (16-bit integers)
> internally:
>
> >>> QtGui.QColor.fromRgbF(0.5, 0.5, 0.5)
>> PyQt6.QtGui.QColor(128, 128, 128)
>> >>> QtGui.QColor.fromRgbF(0.5, 0.5, 0.501)
>> PyQt6.QtGui.QColor(128, 128, 128)
>> >>> QtGui.QColor.fromRgbF(0.5, 0.5, 0.5) == QtGui.QColor.fromRgbF(0.5,
>> 0.5, 0.5)
>> True
>> >>> QtGui.QColor.fromRgbF(0.5, 0.5, 0.5) == QtGui.QColor.fromRgbF(0.5,
>> 0.5, 0.501)
>> False
>
>
> As a debugging aid, this would arguably be worse than no repr at all, in
> some cases.
>
> The float constructor lets you specify more accurate values, but since the
> components aren't *stored* as floats, the rounding makes it kind of gross:
>
> >>> QtGui.QColor.fromRgbF(0.5, 0.5, 0.501)
>> PyQt6.QtGui.QColor.fromRgbF(0.5000076293945312, 0.5000076293945312,
>> 0.5009994506835938)
>>
>
> You could use the constructor that takes 16-bit integers:
>
> >>> QtGui.QColor.fromRgbF(0.5, 0.5, 0.501)
>> PyQt6.QtGui.QColor.fromRgba64(32768, 32768, 32833)
>
>
> But that's kind of hard to read at a glance, which is not great given that
> this is supposed to help with debugging.
>
> I think what I'd do, personally, is have it dynamically choose which way
> to repr itself based on whether all the channels match what Qt would choose
> for 8-bit input values (aka channel * 0x101):
>
> >>> QtGui.QColor.fromRgba64(32382, 32639, 32896)
>> PyQt6.QtGui.QColor(126, 127, 128)
>> >>> QtGui.QColor.fromRgba64(32382, 32639, 32897)
>> PyQt6.QtGui.QColor.fromRgba64(32382, 32639, 32897)
>
>
> Shrug. Just my two cents, I guess :)
>
> On Tue, Apr 4, 2023 at 5:40 PM Nyall Dawson <nyall.dawson at gmail.com>
> wrote:
>
>> Hi list!
>>
>> I'm wondering if it would be possible to add a __repr__ for the QColor
>> class. PyQt doesn't set one itself, but it's VERY useful for debugging
>> purposes.
>>
>> Downstream we patch one in using this approach:
>>
>> https://github.com/qgis/QGIS/blob/574d1ea47b921ff9733f75b577e38034bae74793/python/PyQt/PyQt5/QtGui.py#L27
>>
>> Would you consider adding a similar repr to PyQt itself?
>>
>> Many thanks!
>> Nyall
>>
>
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