On 3 May 2018 at 19:15, J Barchan <jnbarchan at gmail.com> wrote:
> 鈥�
>> On 3 May 2018 at 18:24, Phil Thompson <phil at riverbankcomputing.com> wrote:
>>> On 3 May 2018, at 6:16 pm, J Barchan <jnbarchan at gmail.com> wrote:
>> >
>> >
>> >
>> > On 3 May 2018 at 18:01, Phil Thompson <phil at riverbankcomputing.com>
>> wrote:
>> > On 3 May 2018, at 5:32 pm, J Barchan <jnbarchan at gmail.com> wrote:
>> > >
>> > > 鈥嬧�媀ery few contexts in Qt care about null QVariants - this may well
>> be the only one.鈥嬧�� (An invalid QVariant - which mapped to None - is much
>> more common.)
>> > >
>> > > Phil
>> > >
>> > > 鈥婬i Phil,
>> > >
>> > > Thanks, I knew about the return value from
>> 鈥嬧�嬧�嬧�媠ip.enableautoconversion(), I was going to put in your suggestion
>> when I had a moment.
>> > >
>> > > As you have shown it is not necessary in this case. However you would
>> have problems for virtual re-implementations that are passed a QVariant as
>> an argument rather than being passed back as a result.
>> > >
>> > > I don't get this, or we are not quite talking the same language.
>> Until we spotted this issue, the Python override function was causing the
>> wrong result to be returned. We did have to do something in this case: we
>> had to make a call to 鈥媠ip.enableautoconversion(QtCore.QVariant, False),
>> which neither I nor anyone else would have known we were supposed to do
>> here.
>> >
>> > I disagree with that - although I'm not saying that the documentation
>> couldn't be improved.
>> >
>> > > I don't mind how we phrase it, but I just need to know what pattern I
>> might need to look out for if I'm supposed to do similar somewhere else in
>> Qt/PyQt?
>> >
>> > Anywhere that a null QVariant has a specific meaning and is being
>> passed as an argument to a virtual function.
>> >
>> > > Very few contexts in Qt care about null QVariants - this may well be
>> the only one.鈥� (An invalid QVariant - which mapped to None - is much more
>> common.)
>> > >
>> > > I'll take your word for it. All I would say is that this seems to
>> have come about because we are trying to handle the return of NULL from a
>> database --- right? Might there not be more functions among all the
>> data-handling ones where this occurs?
>> >
>> > 鈥嬧�婤y context I mean the QtSql module.
>> >
>> > PyQt's behaviour is a compromise that works in 90+% of cases without
>> having to use autoenableconversion(). Between us we have identified a case
>> where using autoenableconversion() wouldn't solve the problem. However I'm
>> not sure there is an example in Qt.
>> >
>> > Phil
>> >
>> > 鈥嬧��
>> > By context I mean the QtSql module.鈥�
>> >
>> >
>> > 鈥媃es, OK, I did mean "another function in the QtSql module"鈥�
>> >
>> > 鈥�> I don't mind how we phrase it, but I just need to know what pattern
>> I might need to look out for if I'm supposed to do similar somewhere else
>> in Qt/PyQt?
>> >
>> > Anywhere that a null QVariant has a specific meaning and is being
>> passed as an argument to a virtual function.
>> >
>> > 鈥婽his could be very important, I wonder if you're expecting me to
>> understand/be aware of something which you are but I am not....
>> >
>> > I believed what we/I had discovered, specifically in my code not some
>> other code people might write, was a BUG. And you were going to fix in
>> next version so that I should not have to use the
>> 鈥媠ip.enableautoconversion() I have had put in.
>> >
>> > I now wonder whether I have been laboring under a misapprehension, and
>> in fact you are saying my case is effectively expected behaviour, not bug,
>> and the sip.enableautoconversion() I have put in is meant to be there, now
>> and in the future. Is that the case, could you be very explicit about this
>> kindly?
>> >
>> > Unlike the other guy you were debating with in 2016, I'm not wanting to
>> argue with you about what is best or not. I just want to know what I need
>> to do to work properly. I may or may not like it, but if I have to keep an
>> eye out for:
>> >
>> > Anywhere that a null QVariant has a specific meaning and is being
>> passed as an argument to a virtual function [EDIT: or returned from one in
>> the case I show, right?].
>> >
>> > and that's my responsibility and I may have to use
>> sip.enableautoconversion() explicitly in places, at least I know what's
>> expected from me!!
>>>> There are *two* issues.
>>>> The one that you actually hit is not a bug - it is the expected
>> behaviour. The solution is to use autoconversionenabled() as you are now
>> doing.
>>>> The other is a bug which (at the moment) is theoretical, ie. I'm not
>> aware of a Qt call that would be affected.
>>>> If I fixed the bug then it would also change the behaviour so that you
>> wouldn't need to use autoconversionenabled() - but it wouldn't matter if
>> you still did.
>>>> Phil
>>> 鈥婤rilliant, had 鈥媙ot appreciated that, much clearer.
>> I have one further clarification to request. However, I shall
> deliberately not ask you now, as I think you deserve an evening's rest,
> wherever you are in the world! :) If I may, I'll ask you tomorrow.
>> Thanks for all your time.
>>> --
> Kindest,
> Jonathan
>
鈥婲ow I'm finding that, with the fix discussed, while my overridden function
definition correctly handles database NULLs, it "goes wrong" (as in,
different behaviour from before) in certain other cases, returning a
QVariant where it did not do so before (it returned the converted, native
Python type).鈥�
1. So long as I do not override QSqlQueryModel.data() at all, there is
absolutely no problem --- both database NULL and auto-conversion of non-NULL
to Python native type work fine, and are distinct. *This is the situation
I need.*
2. I need to override QSqlQueryModel.data() for my own purposes. If I
write just:
def data(self, index: QtCore.QModelIndex, role=QtCore.Qt.DisplayRole)
-> typing.Any:
value = super().data(index, role)
return value
Some data conversion happens, such that I no longer get NULL back where the
value is NULL --- instead it is converted to '' if *string* or 0 if
*int*. *This
was my original problem and is not acceptable.*
3. Following our discussion, I change that to:
def data(self, index: QtCore.QModelIndex, role=QtCore.Qt.DisplayRole)
-> typing.Any:
was_enabled = sip.enableautoconversion(QtCore.QVariant, False)
value = super().data(index, role)
sip.enableautoconversion(QtCore.QVariant, was_enabled)
return value
Now I correctly get whatever for database NULL, which works. *However*,
some other path of code, on some quite different non-NULL value, gets back
a QVariant where it used to get a string. I don't know what that path of
code is, but I don't think I should care.
So, what I need is: code which allows me to override QSqlQueryModel.data()
but returns the original data() value *unchanged*, just like it used when I
did not put any override in (case #1). It must do whatever to correctly
deal with NULL & non-NULL, just like the non-overridden
QSqlQueryModel.data() does.
(In PyQt 5.7) *What exact code can I put into the override to achieve just
that, please?* Surely that can be done, no?
--
Kindest,
Jonathan
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‘She has never mentioned her father to me. Was he—well, the sort of man whom the County Club would not have blackballed?’ "We walked by the side of our teams or behind the wagons, we slept on the ground at night, we did our own cooking, we washed our knives by sticking them into the ground rapidly a few times, and we washed our plates with sand and wisps of grass. When we stopped, we arranged our wagons in a circle, and thus formed a 'corral,' or yard, where we drove our oxen to yoke them up. And the corral was often very useful as a fort, or camp, for defending ourselves against the Indians. Do you see that little hollow down there?" he asked, pointing to a depression in the ground a short distance to the right of the train. "Well, in that hollow our wagon-train was kept three days and nights by the Indians. Three days and nights they stayed around, and made several attacks. Two of our men were killed and three were wounded by their arrows, and others had narrow escapes. One arrow hit me on the throat, but I was saved by the knot of my neckerchief, and the point only tore the skin a little. Since that time I have always had a fondness for large neckties. I don't know how many of the Indians we killed, as they carried off their dead and wounded, to save them from being scalped. Next to getting the scalps of their enemies, the most important thing with the Indians is to save their own. We had several fights during our journey, but that one was the worst. Once a little party of us were surrounded in a small 'wallow,' and had a tough time to defend ourselves successfully. Luckily for us, the Indians had no fire-arms then, and their bows and arrows were no match for our rifles. Nowadays they are well armed, but there are[Pg 41] not so many of them, and they are not inclined to trouble the railway trains. They used to do a great deal of mischief in the old times, and many a poor fellow has been killed by them." As dusk came on nearly the whole population of Maastricht, with all their temporary guests, formed an endless procession and went to invoke God's mercy by the Virgin Mary's intercession. They went to Our Lady's Church, in which stands the miraculous statue of Sancta Maria Stella Maris. The procession filled all the principal streets and squares of the town. I took my stand at the corner of the Vrijthof, where all marched past me, men, women, and children, all praying aloud, with loud voices beseeching: "Our Lady, Star of the Sea, pray for us ... pray for us ... pray for us ...!" It had not occurred to her for some hours after Mrs. Campbell had told her of Landor's death that she was free now to give herself to Cairness. She had gasped, indeed, when she did remember it, and had put the thought away, angrily and self-reproachfully. But it returned now, and she felt that she might cling to it. She had been grateful, and she had been faithful, too.[Pg 286] She remembered only that Landor had been kind to her, and forgot that for the last two years she had borne with much harsh coldness, and with a sort of contempt which she felt in her unanalyzing mind to have been entirely unmerited. Gradually she raised herself until she sat quite erect by the side of the mound, the old exultation of her half-wild girlhood shining in her face as she planned the future, which only a few minutes before had seemed so hopeless. After he had gloated over Sergeant Ramsey, Shorty got his men into the road ready to start. Si placed himself in front of the squad and deliberately loaded his musket in their sight. Shorty took his place in the rear, and gave out: The groups about each gun thinned out, as the shrieking fragments of shell mowed down man after man, but the rapidity of the fire did not slacken in the least. One of the Lieutenants turned and motioned with his saber to the riders seated on their horses in the line of limbers under the cover of the slope. One rider sprang from each team and ran up to take the place of men who had fallen. "As long as there's men and women in the world, the men 'ull be top and the women bottom." Then, in the house, the little girls were useful. Mrs. Backfield was not so energetic as she used to be. She had never been a robust woman, and though her husband's care had kept her well and strong, her frame was not equal to Reuben's demands; after fourteen years' hard labour, she suffered from rheumatism, which though seldom acute, was inclined to make her stiff and slow. It was here that Caro and Tilly came in, and Reuben began to appreciate his girls. After all, girls were needed in a house—and as for young men and marriage, their father could easily see that such follies did not spoil their usefulness or take them from him. Caro and Tilly helped their grandmother in all sorts of ways—they dusted, they watched pots, they shelled peas and peeled potatoes, they darned house-linen, they could even make a bed between them. HoME一级毛片视频免费公开
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