How to use the classes.app.get_app function in classes

def actionRenameTrack_trigger(self, event):
        """Callback for renaming track"""
        log.info('actionRenameTrack_trigger')

        # Get translation function
        _ = get_app()._tr

        # Get details of track
        track_id = self.selected_tracks[0]
        selected_track = Track.get(id=track_id)

        # Find display track number
        all_tracks = get_app().project.get("layers")
        display_count = len(all_tracks)
        for track in reversed(sorted(all_tracks, key=itemgetter('number'))):
            if track.get("id") == track_id:
                break
            display_count -= 1

        track_name = selected_track.data["label"] or _("Track %s") % display_count

        text, ok = QInputDialog.getText(self, _('Rename Track'), _('Track Name:'), text=track_name)

def save_project(self, file_path):
        """ Save a project to a file path, and refresh the screen """
        app = get_app()
        _ = app._tr  # Get translation function

        try:
            # Update history in project data
            s = settings.get_settings()
            app.updates.save_history(app.project, s.get("history-limit"))

            # Save project to file
            app.project.save(file_path)

            # Set Window title
            self.SetWindowTitle()

            # Load recent projects again
            self.load_recent_menu()

def update_model(self, clear=True):
        log.info("updating effects model.")
        app = get_app()

        # Get window to check filters
        win = app.window
        _ = app._tr

        # Clear all items
        if clear:
            self.model_names = {}
            self.model.clear()

        # Add Headers
        self.model.setHorizontalHeaderLabels([_("Thumb"), _("Name"), _("Description")])

        # Get the folder path of effects
        effects_dir = os.path.join(info.PATH, "effects")
        icons_dir = os.path.join(effects_dir, "icons")

def ShowTransitionMenu(self, tran_id=None):
        log.info('ShowTransitionMenu: %s' % tran_id)

        # Get translation method
        _ = get_app()._tr

        # Get existing transition object
        tran = Transition.get(id=tran_id)
        if not tran:
            # Not a valid transition id
            return

        # Set the selected transition (if needed)
        if tran_id not in self.window.selected_transitions:
            self.window.addSelection(tran_id, 'transition')
        # Get list of all selected transitions
        tran_ids = self.window.selected_transitions
        clip_ids = self.window.selected_clips

        # Get framerate
        fps = get_app().project.get(["fps"])

def showDocks(self, docks):
        """ Show all dockable widgets on the main screen """
        for dock in docks:
            if get_app().window.dockWidgetArea(dock) != Qt.NoDockWidgetArea:
                # Only show correctly docked widgets
                dock.show()

from classes.app import get_app
        import openshot
        import json

        # Get translation method
        _ = get_app()._tr

        # Append version info
        v = openshot.GetVersion()
        project_data = {}
        project_data["version"] = {"openshot-qt" : info.VERSION,
                                   "libopenshot" : v.ToString()}

        # Get FPS from project
        from classes.app import get_app
        fps = get_app().project.get("fps")
        fps_float = float(fps["num"]) / float(fps["den"])

        # Import legacy openshot classes (from version 1.X)
        from classes.legacy.openshot import classes as legacy_classes
        from classes.legacy.openshot.classes import project as legacy_project
        from classes.legacy.openshot.classes import sequences as legacy_sequences
        from classes.legacy.openshot.classes import track as legacy_track
        from classes.legacy.openshot.classes import clip as legacy_clip
        from classes.legacy.openshot.classes import keyframe as legacy_keyframe
        from classes.legacy.openshot.classes import files as legacy_files
        from classes.legacy.openshot.classes import transition as legacy_transition
        from classes.legacy.openshot.classes import effect as legacy_effect
        from classes.legacy.openshot.classes import marker as legacy_marker
        sys.modules['openshot.classes'] = legacy_classes
        sys.modules['classes.project'] = legacy_project
        sys.modules['classes.sequences'] = legacy_sequences

def __init__(self):

        # Create dialog class
        QDialog.__init__(self)

        # Load UI from designer
        ui_util.load_ui(self, self.ui_path)

        # Init UI
        ui_util.init_ui(self)

        # Track metrics
        track_metric_screen("animated-title-screen")

        # Add render button
        app = get_app()
        _ = app._tr
        self.btnRender = QPushButton(_('Render'))
        self.btnCancel = QPushButton(_('Cancel'))
        self.buttonBox.addButton(self.btnRender, QDialogButtonBox.AcceptRole)
        self.buttonBox.addButton(self.btnCancel, QDialogButtonBox.RejectRole)

        # Add blender treeview
        self.blenderTreeView = BlenderListView(self)
        self.verticalLayout.addWidget(self.blenderTreeView)

        # Init variables
        self.unique_folder_name = str(uuid.uuid1())
        self.output_dir = os.path.join(info.USER_PATH, "blender")
        self.selected_template = ""
        self.is_rendering = False
        self.my_blender = None

def open_project(self, file_path, clear_thumbnails=True):
        """ Open a project from a file path, and refresh the screen """

        app = get_app()
        _ = app._tr  # Get translation function

        # First check for empty file_path (probably user cancellation)
        if not file_path:
            # Ignore the request
            return

        # Do we have unsaved changes?
        if get_app().project.needs_save():
            ret = QMessageBox.question(self, _("Unsaved Changes"), _("Save changes to project first?"), QMessageBox.Cancel | QMessageBox.No | QMessageBox.Yes)
            if ret == QMessageBox.Yes:
                # Save project
                self.actionSave.trigger()
            elif ret == QMessageBox.Cancel:
                # User canceled prompt
                return

def showDocks(self, docks):
        """ Show all dockable widgets on the main screen """
        for dock in docks:
            if get_app().window.dockWidgetArea(dock) != Qt.NoDockWidgetArea:
                # Only show correctly docked widgets
                dock.show()