In this blog post, we will explore how to use PyQt’s QThread class to implement multithreading in Python. Multithreading allows us to perform multiple tasks simultaneously, improving the responsiveness and performance of our applications.

What is multithreading?

Multithreading is a way to achieve concurrent execution of multiple tasks within a single process. In the context of GUI applications, it helps prevent the user interface from freezing or becoming unresponsive while performing time-consuming tasks such as database operations, network requests, or heavy computations.

PyQt’s QThread class

PyQt provides the QThread class, which allows us to create worker threads in our applications. These worker threads can run in parallel to the main thread, enabling us to perform tasks asynchronously.

To use QThread, we need to subclass it and override the run() method. The run() method contains the code that will be executed in the background thread.

Let’s take a look at an example:

from PyQt5.QtCore import QThread

class WorkerThread(QThread):
    def run(self):
        # Perform time-consuming task here
        pass

In the example above, we have created a subclass of QThread called WorkerThread. We override the run() method to define the task that will be executed in the background thread.

Starting the thread

To start our QThread, we need to create an instance of our custom thread class and call the start() method. Here’s an example of how to start the thread:

worker = WorkerThread()
worker.start()

Once the thread is started, the run() method will be executed in the background thread.

Signals and slots

One of the advantages of using QThread is that it provides a mechanism for inter-thread communication using signals and slots. We can emit signals from the worker thread and connect them to slots in the main thread to update the user interface or perform other tasks.

To define a signal in our custom thread class, we use the pyqtSignal class. Here’s an example:

from PyQt5.QtCore import QThread, pyqtSignal

class WorkerThread(QThread):
    finished = pyqtSignal()

    def run(self):
        # Perform time-consuming task here
        self.finished.emit()

In the example above, we have defined a finished signal that will be emitted when the task is completed in the run() method.

To connect the signal to a slot in the main thread, we use the connect() method. Here’s an example:

worker = WorkerThread()
worker.finished.connect(my_slot_function)
worker.start()

In the example above, we connect the finished signal of the worker thread to a slot function called my_slot_function.

Conclusion

In this blog post, we have learned how to use PyQt’s QThread class to implement multithreading in Python. We saw how to create a custom thread class, start the thread, and use signals and slots for inter-thread communication. Using multithreading can greatly improve the responsiveness and performance of our PyQt applications.