How to pass a value from one class to another where each class is on different file

[SGaist]

There's no triggered signal anywhere in sight in your code.

What can you do ?

Create minimal script with a small UI where you can actually properly experiment and implement signals and slots rather than trying to cram it in your huge code base. Once you have understood how it working, then you will be able to translate that to your application.

On a side note, please give your classes and variable meaningful names. Random things like class_1 does not make your code readable nor easy to reason about.

[john_hobbyist]

@SGaist said in How to pass a value from one class to another where each class is on different file:

There's no triggered signal anywhere in sight in your code.

What can you do ?

Create minimal script with a small UI where you can actually properly experiment and implement signals and slots rather than trying to cram it in your huge code base. Once you have understood how it working, then you will be able to translate that to your application.

On a side note, please give your classes and variable meaningful names. Random things like class_1 does not make your code readable nor easy to reason about.

I have spent many days studying tutorials such as this: https://programmer.group/pyqt5-quick-start-pyqt5-signal-slot-mechanism.html, this: https://www.geeksforgeeks.org/pyqt5-qaction/ and many stackoverflow questions.... What I mean is that I have ran code and see what happens. Do I need these lines from the code above:

# in `MainWindow` class, somewhere
self.window1 = class_1()
self.window2 = class_2()

???

[SGaist]

That's quite a strange question to ask. If you want to use objects from either of class_1 or class_2 in your MainWindow class, then yes you need them.

[john_hobbyist]

@SGaist said in How to pass a value from one class to another where each class is on different file:

That's quite a strange question to ask. If you want to use objects from either of class_1 or class_2 in your MainWindow class, then yes you need them.

So, since

triggered.connect

does not work on them, how I send the signal when the menus (that call those functions) are chosen? I am confused...

[JonB]

@john_hobbyist said in How to pass a value from one class to another where each class is on different file:

does not work on them, how I send the signal when the menus (that call those functions) are chosen? I am confused...

Q: What Qt object has a triggered signal?
A: void QAction::triggered(bool checked = false)

This signal is emitted when an action is activated by the user; for example, when the user clicks a menu option, toolbar button, or presses an action's shortcut key combination, or when trigger() was called

So you need QActions for your QMenu items:

Normally, you connect each menu action's triggered() signal to its own custom slot

[john_hobbyist]

I left signals and slots. I am trying with getters and setters... like here: https://www.geeksforgeeks.org/getter-and-setter-in-python/

I have stuck here... This is part of my code:

class class_1():
	def do_this(self):
		...
		# code here...
		...
		self.myvar = "Ok"
		...
	def get_var(self):
		return self.myvar

class class_2():
	def do_something(self):
		raj = class_1()
		self.var = raj.get_var()
		print("var = ", self.var) # here I check the value
		...

But I get this error:

    raj = class_1()
UnboundLocalError: local variable 'class_1' referenced before assignment

Any idea what I miss here?

[JonB]

@john_hobbyist

• Did you import the class1 module into the class_2 module?
• Is your code indeed as you show?
• Does it really say it fails on the raj = class_1() statement?
• Are you aware, even if you get this working, that raj = class_1() will create a new instance of class_1? And that is really what you intend/need for your question, and you're not going to come back and say "but this way it doesn't access the existing class_2 instance/widget I had"... ?

[SGaist]

Beside the points of @JonB, please write a minimal complete script that we can take a look at. You only post small snipets from here and there then some error that we can only vaguely guess why they happen.

[john_hobbyist]

@JonB said in How to pass a value from one class to another where each class is on different file:

@john_hobbyist

• Did you import the class1 module into the class_2 module?
• Is your code indeed as you show?
• Does it really say it fails on the raj = class_1() statement?
• Are you aware, even if you get this working, that raj = class_1() will create a new instance of class_1? And that is really what you intend/need for your question, and you're not going to come back and say "but this way it doesn't access the existing class_2 instance/widget I had"... ?

Thank you for your comment! No, my code is very huge. I depict only the needed parts here... Do you have any better idea of how to pass the value from class_1() to class_2()? I tried signals/slots but I didn't achieve something. Any idea of how to pass the value with getters/setters?

[SGaist]

You realize to you linked to a blog post describing exactly how to implement a getter and a setter and how to use them ?

[john_hobbyist]

@SGaist said in How to pass a value from one class to another where each class is on different file:

You realize to you linked to a blog post describing exactly how to implement a getter and a setter and how to use them ?

I tried to follow the link but as you see above I face problems with my code...

[SGaist]

As already written earlier, the fact that you post snipets of parts of your code distributed makes it almost impossible to help you.

As @JonB already suggested: you likely did not import class_1 properly in the file where you define class_2.

[lanas]

i do not know if there is a predefined method in PyQt but in python you can get the value from a function and call it in other class
this is a simple prototype may helps you

def idfunc(self):
       id =self.user_idtext()
     
       return id

[SGaist]

@lanas PyQt is a set of Python bindings for the Qt framework, it does not do special things outside of the Python realm. The same rules apply.

[john_hobbyist]

@SGaist said in How to pass a value from one class to another where each class is on different file:

As already written earlier, the fact that you post snipets of parts of your code distributed makes it almost impossible to help you.

As @JonB already suggested: you likely did not import class_1 properly in the file where you define class_2.

Yes, I do! Nothing works! Apart from signals/slots and getters/setters how can I pass the value from class_1 to class_2? class_1 and class_2 are stored in different files...

[SGaist]

Well, this is the standard way to do it.

The fact that your classes are in two different files just means that you have to use proper imports to be able to use them. Nothing more.

From the looks of it, you essentially need to clean up your code base.

As suggested earlier, you should write a small dummy project that does what you want and then adapt that to your big code base.

[john_hobbyist]

@SGaist said in How to pass a value from one class to another where each class is on different file:

Well, this is the standard way to do it.

The fact that your classes are in two different files just means that you have to use proper imports to be able to use them. Nothing more.

From the looks of it, you essentially need to clean up your code base.

As suggested earlier, you should write a small dummy project that does what you want and then adapt that to your big code base.

I tried this: https://www.geeksforgeeks.org/getter-and-setter-in-python/ and this: https://programmer.group/pyqt5-quick-start-pyqt5-signal-slot-mechanism.html that have source code. I will try again

[john_hobbyist]

@JonB : What's the purpose of these lines:

# in `MainWindow` class, somewhere
self.window1 = class_1()
self.window2 = class_2()

?

[JonB]

@john_hobbyist
In the example, class_1 & class_2 are each some kind of widget/window classes, each derived from QWidget. class_1() & class_2() each create a new instance (window in this case) of the respective class. I store the references in two member variables of self, perhaps your MainWindow class.

[john_hobbyist]

I am working on this: https://doc.qt.io/qtforpython/examples/example_widgets__thread_signals.html which is perfect for what I want to achieve because it has int signals and includes 3 classes. I am trying to divide it on 3 files. Each class on a separate file and import the other 2 classes from the files. But I get the following error:

(most likely due to a circular import)

How would you divide it?