[Pyside2] Multiple QLineEdit signals not working

Geoffrey

Hi !
Sorry in advance for my english, it's not my main language.

I try to have this code : objQLineEdit.signal.connect(self.function) working under a for loop.
For testing, i just use a simple print.

For example with this :

for i in range(10):
objQLineEdit = QLineEdit()
objQLineEdit.signal.connect(lambda: self.function(objQLineEdit.text()))
<END CODE>

Only the last QLineEdit has a signal that is working.
How can i get all of them work ?

Thank's in advance.

JonB

@Geoffrey said in [Pyside2] Multiple QLineEdit signals not working:

Only the last QLineEdit has a signal that is working.

I do not believe that is so. Replace by:

objQLineEdit.signal.connect(lambda: print("Some signal"))

(I don't know what your particular objQLineEdit.signal is, I presume you have something like clicked there, not actually signal. I assume your whole code is an "outline", not real code.)

Does that indeed print when any of the edits are pressed? I believe it should.

What you may have a problem with in Python is your particular lambda:

objQLineEdit.signal.connect(lambda: self.function(objQLineEdit.text()))

I'm not 100% about this, but I think that will only ever pass the last value of objQLineEdit. Try:

objQLineEdit.signal.connect(lambda lineEdit=objQLineEdit: self.function(lineEdit.text()))

If that works, this is a Python-esque issue.

Geoffrey

@JonB

You are right ! It was indeed the lambda the real problem.
And yes it is an "outline" code.

Thank you its working ! :)

JonB

@Geoffrey
This business of needing in Python to write:

for objQLineEdit in ...:
    objQLineEdit.signal.connect(lambda lineEdit=objQLineEdit: self.function(lineEdit.text()))

really threw me when I first came across it. It works differently from the C++ lambda:

connect(objQLineEdit,  &Class::signal, [objQLineEdit]() { qDebug() << objLineEdit.text(); });

In the C++ you get the lambda's objLineEdit to be the current value of objQLineEdit when it was set up, like you'd expect.

But in the Python

objQLineEdit.signal.connect(lambda: self.function(objQLineEdit.text()))

you get all the lambdas connecting to the last value objQLineEdit had when the loop was run. Passing it as a parameter to the lambda by

objQLineEdit.signal.connect(lambda lineEdit=objQLineEdit: self.function(lineEdit.text()))

seems to be the equivalent of the C++ lambda, so that it references the objQLineEdit as it was when the line was executed.

Keep this in mind, as it comes up again whenever you write Python lambdas in Qt! :)

Geoffrey

@JonB said in [Pyside2] Multiple QLineEdit signals not working:

@Geoffrey
This business of needing in Python to write:
for objQLineEdit in ...:
    objQLineEdit.signal.connect(lambda lineEdit=objQLineEdit: self.function(lineEdit.text()))
really threw me when I first came across it.

I have the same reaction :p

Keep this in mind, as it comes up again whenever you write Python lambdas in Qt! :)

Yes i try to not reproduce twice the same mistake and learn from it :)