Qt connect and first connect or unicode

[Steven D'Aprano]

On Tue, 17 Sep 2013 08:42:35 +0430, Mohsen Pahlevanzadeh wrote:

> Dear all,
> 
> Unfortunately, i confused and need help... the following code is:
> ################################################### 
> ##CheckBox:
>     QtCore.QObject.connect(self.checkBox,
> QtCore.SIGNAL(_fromUtf8("toggled(bool)")), lambda:
> self.materialsInstance.setFilterDict("C", self, "name",
> self.lineEdit.text()))


I don't use Qt, but I'll try to help.

First question, what does _fromUtf8 do? It appears to be a private 
function. Is that your function? If you want to create a string from UTF-8 
bytes, use:

some_bytes.decode('utf-8')

I don't think there is a need for a dedicated _fromUtf8 function.

If you are using Python 3, then "toggled(bool)" is already a Unicode 
string, and there is no need to convert from UTF-8.

If you are using Python 2, then "toggled(bool)" is a byte string, and you 
can turn it into a Unicode string by just using the u prefix:

u"toggled(bool)"

Again, no need to convert from UTF-8.

The only time you need to convert from UTF-8 is when you are reading data 
from a file, or other external source, that is encoded in UTF-8.

Other than that, your first line of code seems like a straight-forward 
call to set a callback function. When the button is pressed, the 
instance's attribute materialsInstance calls the method setFilterDict.


>         QtCore.QObject.connect(self.checkBox_2,
> QtCore.SIGNAL(_fromUtf8("toggled(bool)")), lambda:
> self.materialsInstance.setFilterDict("C", self, "bought_price",
> persianToInteger(unicode(self.lineEdit_2.text()))))

Again, the same method is called, only this time with different 
arguments. Hmmm, this strikes me as poor design. I think that a better 
design would be for the object to have a few methods:

    def toggle_checkbox(self, flag):
        # checkbox logic goes here, e.g.
        if flag:
            ...
        else:
            ...

And then your callback is trivially

lambda: self.toggle_checkbox(get_state)


I'm not sure how to get the checkbox state from Qt, you will need to 
replace the "get_state" with the correct code.

That, in my opinion, is easier to understand.


>         QtCore.QObject.connect(self.checkBox_4,
> QtCore.SIGNAL(_fromUtf8("toggled(bool)")), lambda:
> self.materialsInstance.setFilterDict("C",self,"stock",
> persianToInteger(unicode(self.lineEdit_3.text()))))

And more callbacks. Most of your code is probably irrelevant to the 
problem you are having. You will help us to help you if you can read this 
website:

http://sscce.org/


and simplify your code.


[...many more callbacks...]


> #################################################### 
> Description:
> I have 3 widget:
> 1. CheckBox:  a. name b. bought_price c. stock 2. LineEdit : a. name b.
> bought_price c. stock 3. One PushButton
> 
> i have three slot: 1. responseToRequestForData()  2.setFilterDict()
> 3.unSetFilterDict()
> responseToRequestForData(): start to search in DB setFilterDict(): fill
> a dict from my LineEdit
> 
> Problem:
> My name is filled in dict but its value doesn't fill up. b and c don't
> have any problem.

I'm afraid I don't understand this. Even your followup post doesn't 
really help:

> I see same output in console:
> {'stock': 2, 'name': PyQt4.QtCore.QString(u''), 'bought_price': 23}


What result where you expecting?

If I remember correctly, Qt strings are mutable unicode strings, so 
'name' is associated with an empty Qt string. If they are mutable, that 
means that once the dict is set:

{'name': QString(u'contents of text field'), ...}


if the text field changes, so will the string. Is that what is happening?

(Or perhaps I have mis-remembered about Qt strings.)

You have two callbacks that appear to set the "name" key in the dict. 
Perhaps one of them is setting it to an empty value.




-- 
Steven