[PyQt] Using Qt to emit a signal (or maybe with QTimer)

[pyhill00]

I am trying to send an .hdf5 file to a method in the main python file in the class here:

    class DesignerMainWindow(QtGui.QMainWindow, Ui_MainWindow):
        """Customization for Qt Designer created window"""
    
        signal_output_log = QtCore.Signal("QString")
        sig_clear_log = QtCore.Signal()
    
        def __init__(self, parent=None):
            super(DesignerMainWindow, self).__init__(parent)
            self.setupUi(self)
            self.image_analyzer = ImageAnalyzer(self)
            self.listener = watchdog_search.ObserverWrapper("/home/Test_Data/")
            self.on_finished_run(self.listener.wait_for_file())
        def on_finished_run(self, tuple: ()):
            self.image_analyzer.load_image(str(tuple[0]), str(tuple[1]), from_remote=True)

The .hdf5 file comes from this `watchdog_search.py:

    import time
    import traceback
    import os

    import h5py
    import queue
    from typing import Union

    from watchdog.observers import Observer
    from watchdog.events import FileSystemEventHandler, DirCreatedEvent, FileCreatedEvent


    class NewFileHandler(FileSystemEventHandler):
        """h5 file creation handler for Watchdog"""

        def __init__(self):
            self.file_queue = queue.Queue()

        # callback for File/Directory created event, called by Observer.
        def on_created(self, event: Union[DirCreatedEvent, FileCreatedEvent]):
            if event.src_path[-4:] == "hdf5":
                # run callback with path string
                self.file_queue.put(event.src_path)


    class ObserverWrapper:
        """Encapsulated Observer boilerplate"""

        def __init__(self, path: str, recursive=True):
            self.path = path
            self.recursive = recursive

            self.observer = Observer()
            self.handler = NewFileHandler()

            self.observer.schedule(self.handler, path=path, recursive=recursive)

            self.start()

        def start(self):
            """
            Starts observing for filesystem events. Runs self.routine() every 1 second.

            :param blocking: If true, blocks main thread until keyboard interrupt.
            """

            self.observer.start()
        def stop(self):
            """
            Stops the observer. When running self.start(blocking=True) then you don't need to call this.
            """

            self.observer.stop()
            self.observer.join()

        def wait_for_file(self):
            """
            Wait and Process newly created files
            """

            max_retry_count = 3500 # for test purposes now but want to set an upper bound on verifying a file is finished.
            # will try h5 file for a max of 35 seconds (upper bound) to see if the file is finished.
            # Files are usually finished within 20-30 seconds
            #
            retry_interval_seconds = .01 # every hundreth it will try the file to see if it finished writing

            # wait for file to be added
            #print(self.handler.file_queue.get(block=True))
            file_path = self.handler.file_queue.get(block=True)
            file_name = os.path.basename(file_path)

            # try to open the file
            retry_count = 0
            while True:
                try:
                    file = h5py.File(file_path, "r")
                    file.close()
                    return file_path, file_name
                except OSError:
                    if retry_count < max_retry_count:
                        retry_count += 1
                        print(f"h5 file <{file_path}> is locked, retrying {retry_count}/{max_retry_count}")
                        time.sleep(retry_interval_seconds)
                    else:
                        print(f"h5 file <{file_path}> reached max retry count, skipping")

                except Exception as err:
                    print(f"Got unexpected Error <{type(err).__name__}> while opening <{file_path}> ")
                    traceback.print_exc()

Currently I call this file by

    self.listener = watchdog_search.ObserverWrapper("/path/to/folder/of/interest")

in the main.py file but this only sends one hdf5 file and doesn't send any more. Watchdog needs to stay open and send content to main.py every time there is a new hdf5 file available. Does anyone know how to use Qt to do this? I was also thinking about using QTimer but I am not sure how this would work exactly. This is not a question of watchdog but rather a question of asynchronous programming and Qt. I need at the end to send the file_path and file_name of the .hdf5 to on_finished_run() or perhaps have on_finished_run() be the subscriber for the signal but I am unsure how to do this when the try returns not the emitted signal but rather the file path and name. Any insight is greatly appreciated.

[deanhystad]

I took this answer for a related question.

https://stackoverflow.com/questions/6884...hdog-on-qt

And maybe modified it to work with your code. I do not have the watchdog module installed and I don't know anything about your image analyzer. Really untested code here:

# Many imports

class Bridge(QtCore.QObject):
    '''Serves as a bridge between watchdog thread and Qt thread'''
    created = QtCore.Signal(FileSystemEvent)


class Handler(FileSystemEventHandler):
    '''watchdog observer event handler'''
    def __init__(self):
        super().__init__()
        self.bridge = Bridge()

    def on_created(self, event):
        '''Emit signal when hdf5 file is created'''
        if event.src_path[-4:] == 'hdf5':
            self.bridge.created.emit(event)


class MyMainWindow(QtGui.QMainWindow, Ui_MainWindow):
    """My designer created window"""

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

        ...

        # Create observer to signal my new_file method when an
        # hdf5 file is created in path.
        handler = Handler()
        handler.bridge.created.connect(self.new_file)
        observer = Observer()
        observer.schedule(handler, path, recursive=True)
        observer.start()

    def new_file(self, event):
        '''Method called when hdf5 file is created.  Passed a FileSystemEvent'''
        print(event.src_path)
        ...

def main():
    path = ...
    app = QtWidgets.QApplication()
    form = MyMainWindow(path)
    form.show()
    app.exec_()

if __name__ == '__main__':
    main()