Python GUIs: Multithreading PySide6 applications with QThreadPool — Run background tasks concurrently without impacting your UI

When building Python GUI applications with PySide6, the interface can "lock up" when performing long-running background tasks. This is because the event loop that handles user interaction, signals, and timers is driven by events and runs in the same thread as the Python code. Any execution triggered by the event loop will run synchronously within this thread, causing the GUI to freeze if the task takes a long time. To avoid this, long-running tasks should be moved out of the GUI thread into another thread. A minimal stub application is provided to demonstrate multi-threaded execution in PySide6. The wrong approach to solving this issue is to use the processEvents() method, which can cause unpredictable behavior and undefined results. Instead, threads and processes can be used to run independent tasks within a PySide6 application. Qt provides a straightforward interface for running jobs or tasks in other threads using QRunnable and QThreadPool. This approach allows for easy queuing and execution of workers and retrieval of results. By using QThreadPool, the application can handle long-running tasks without freezing the GUI.