How to interrupt a script execution on a QThread in Python PyQt?

Question

What I'm Doing:

I'm making a PyQt app that allows users to select a script file from their machine, the app then executes it using exec() on a separate QThread then shows them the results. I've already implemented all that, and now I'm trying to add a "Stop Executing" button.

The Problem:

I'm not able to interrupt the script execution, which should happen whenever the user presses the "Stop Executing" button. I can't stop the QObject 's task that's executing the script or terminate the QThread that's hosting the object.

My Code:

from PyQt5.QtWidgets import QMainWindow
from PyQt5.QtCore import QObject, QThread

class Execute(QObject):
    def __init__(self, script):
        super().__init__()
        self.script = script

    def run(self):
        exec(open(self.script).read())

class GUI(QMainWindow):
    # Lots of irrelevant code here ...

    # Called when "Start Executing" button is pressed
    def startExecuting(self, user_script):
        self.thread = QThread()
        self.test = Execute(user_script)
        self.test.moveToThread(self.thread)
        self.thread.started.connect(self.test.run)
        self.thread.start()

    # Called when "Stop Executing" button is pressed
    def stopExecuting(self):
        # Somehow stop script execution

My Attempts:

There's a ton of question related to stopping an exec() or a QThread , but none of them work in my case. Here's what I've tried:

1. Calling thread.quit() from GUI (kills thread after script execution ends - same with wait() )
2. Raising a SystemExit from object (exits the whole app after script execution ends)
3. Calling thread.terminate() from GUI (app crashes when "Stop Executing" button is pressed)
4. Using a termination flag variable (not applicable in my case as run() isn't loop based)

---

So, is there any other solution to stop the exec() or kill the thread right when the button is pressed?

Answer 1

Thank's to @ekhumoro's hint about using multiprocessing instead of multithreading, I was able to find a solution.

I used a QProcess to execute the script, and then called process.kill() when the "Stop Executing" button is clicked. Like so:

from PyQt5.QtWidgets import QMainWindow
from PyQt5.QtCore import QProcess

class GUI(QMainWindow):
    # Lots of irrelevant code here ...

    # Called when "Start Executing" button is pressed
    def startExecuting(self, user_script):
        self.process = QProcess()
        self.process.setProcessChannelMode(QProcess.MergedChannels)
        self.process.start("python", ["-u", user_script])

    # Called when "Stop Executing" button is pressed
    def stopExecuting(self):
        self.process.kill()

This stops the script execution right away without interrupting the GUI process, which's exactly what I was looking for.

Answer 2

Check next code, maybe it can help you:

from PyQt5.QtWidgets import QMainWindow
from PyQt5.QtCore    import QObject, QThread
from PyQt5           import Qt               #+


class WorkThread(Qt.QThread):

    threadSignal = Qt.pyqtSignal(int)  

    def __init__(self): 
        super().__init__()

    def run(self, *args, **kwargs):
        c = 0 
        while True:
            Qt.QThread.msleep(100)                    
            c += 1                                    
            self.threadSignal.emit(c)                 


class MsgBox(Qt.QDialog):
    def __init__(self):
        super().__init__()

        layout     = Qt.QVBoxLayout(self)
        self.label = Qt.QLabel("")
        layout.addWidget(self.label)
        close_btn  = Qt.QPushButton("Close")
        layout.addWidget(close_btn)

        close_btn.clicked.connect(self.close) 

        self.setGeometry(900, 65, 400, 80)
        self.setWindowTitle('MsgBox from WorkThread')        


class GUI(Qt.QWidget):     #(QMainWindow):

    def __init__(self):
        super().__init__()

        layout   = Qt.QVBoxLayout(self)
        self.btn = Qt.QPushButton("Start thread.")
        layout.addWidget(self.btn)
        self.btn.clicked.connect(self.startExecuting)

        self.msg    = MsgBox()  
        self.thread = None
        # Lots of irrelevant code here ...

    # Called when "Start/Stop Executing" button is pressed
    def startExecuting(self, user_script):

        if self.thread is None:                     
            self.thread = WorkThread()

            self.thread.threadSignal.connect(self.on_threadSignal)
            self.thread.start()                     

            self.btn.setText("Stop thread")         
        else:
            self.thread.terminate()         
            self.thread = None
            self.btn.setText("Start thread")


    def on_threadSignal(self, value):
        self.msg.label.setText(str(value))
        if not self.msg.isVisible():        
            self.msg.show()        


if __name__ == '__main__':
    app = Qt.QApplication([])
    mw  = GUI()
    mw.show()
    app.exec()