On Tuesday 05 October 2010, 18:20:30 Phil Thompson wrote:
> On Tue, 5 Oct 2010 18:07:25 +0200, "Hans-Peter Jansen" <h...@urpla.net>
>
> wrote:
> > On Tuesday 05 October 2010, 17:34:36 Phil Thompson wrote:
> >> On Tue, 5 Oct 2010 10:42:43 +0200, "Hans-Peter Jansen" <h...@urpla.net>
> >>
> >> > here's another nice example for the collection.
> >> >
> >> > LightMaps
> >>
> >> Thanks - it will be in tonight's snapshot.
> >>
> >> > Phil: it might be a good idea to consider adding __hash__ to
> >> > assorted Qt
> >> >
> >> > classes in order to improve their pythonic appearance, e,g, QPoint,
> >>
> >> QRect,
> >>
> >> > QColor. What do you think?
> >>
> >> __hash__ is implemented for all classes that implement qHash(). I
>
> assume
>
> >> that that covers the sensible ones.
> >
> > Unfortunately qHash(QPoint) is missing. :-(
> >
> > What a pity. Would you take one?
>
> No. Raise it as a bug against Qt.
Done: http://bugreports.qt.nokia.com/browse/QTBUG-14263
but please notice, that Qt has an advantage in this area, since with C++ you
only need to define a qHash function somewhere in your code with the right
signature to be used automatically (well, I guess, the compiler will throw
an error, if it is misssing), while this won't work with PyQt, where this
silently breaks, and I can imagine, that you don't want to pick up qHash
dynamically ;-).
>>> from PyQt4.QtCore import *
>>> d = {}
>>> for i in range(10):
... p = QPoint(42, 42)
... d[p] = True
...
>>> print d
{PyQt4.QtCore.QPoint(42, 42): True, PyQt4.QtCore.QPoint(42, 42): True,
PyQt4.QtCore.QPoint(42, 42): True, PyQt4.QtCore.QPoint(42, 42): True,
PyQt4.QtCore.QPoint(42, 42): True, PyQt4.QtCore.QPoint(42, 42): True,
PyQt4.QtCore.QPoint(42, 42): True, PyQt4.QtCore.QPoint(42, 42): True,
PyQt4.QtCore.QPoint(42, 42): True, PyQt4.QtCore.QPoint(42, 42): True}
>>>
>>> class Point(QPoint):
... def __init__(self, *par):
... if par:
... super(Point, self).__init__(*par)
... else:
... super(Point, self).__init__()
...
... def __hash__(self):
... return self.y() << 24 + self.x()
...
>>> d = {}
>>> for i in range(10):
... p = Point(42, 42)
... d[p] = True
...
>>> print d
{PyQt4.QtCore.QPoint(42, 42): True}
>>>
Anyway, here's the diff for the example to remove the silly C++ qHash
appendix, but adopt it accordingly in the Point.__hash__ method.
Pete
--- ./lightmaps-2.py 2010-10-05 10:13:07.601486236 +0200
+++ ./lightmaps.py 2010-10-05 19:25:10.493646218 +0200
@@ -27,13 +27,10 @@ HOLD_TIME = 701
# Hint: see above to find why I picked self one :)
MAX_MAGNIFIER = 229
-
-def qHash(p):
- return p.x() * 17 ^ p.y()
-
# tile size in pixels
TDIM = 256
+
class Point(QtCore.QPoint):
"""QPoint, that is fully qualified as a dict key"""
def __init__(self, *par):
@@ -43,7 +40,7 @@ class Point(QtCore.QPoint):
super(Point, self).__init__()
def __hash__(self):
- return self.y() << 24 + self.x()
+ return self.x() * 17 ^ self.y()
def __repr__(self):
return "Point(%s, %s)" % (self.x(), self.y())
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