How to use the vaex.events.Signal function in vaex

def __init__(self, ds, **kwargs):
        super(VizBaseState, self).__init__(**kwargs)
        self.ds = ds
        self.signal_slice = vaex.events.Signal()
        self.signal_regrid = vaex.events.Signal()

def __init__(self, thread_pool=None, buffer_size=None, thread_mover=None):
		self.thread_pool = thread_pool or vaex.multithreading.ThreadPoolIndex()
		self.task_queue = []
		self.buffer_size = buffer_size or buffer_size_default
		self.signal_begin = vaex.events.Signal("begin")
		self.signal_progress = vaex.events.Signal("progress")
		self.signal_end = vaex.events.Signal("end")
		self.signal_cancel = vaex.events.Signal("cancel")
		self.thread_mover = thread_mover or (lambda fn, *args, **kwargs: fn(*args, **kwargs))
		self._is_executing = False
		self.lock = threading.Lock()
		self.thread = None

def __init__(self, name, column_names, executor=None):
		self.name = name
		self.column_names = column_names
		self.executor = executor or main_executor
		self.signal_pick = vaex.events.Signal("pick")
		self.signal_sequence_index_change = vaex.events.Signal("sequence index change")
		self.signal_selection_changed = vaex.events.Signal("selection changed")
		self.signal_active_fraction_changed = vaex.events.Signal("active fraction changed")

		self.undo_manager = vaex.ui.undo.UndoManager()
		self.variables = collections.OrderedDict()
		self.variables["pi"] = np.pi
		self.variables["e"] = np.e
		self.virtual_columns = collections.OrderedDict()
		self._length = None
		self._full_length = None
		self._active_fraction = 1
		self._current_row = None

		self.mask = None # a bitmask for the selection does not work for server side
		self._has_selection = False

def __init__(self, parent):
        super(DatasetSelector, self).__init__(parent)
        # self.icon = QtGui.QIcon('icons/png/24x24/devices/memory.png')
        # self.icon_server = QtGui.QIcon('icons/png/24x24/devices/memory.png')
        self.icon = QtGui.QIcon(vp.iconfile('drive'))
        self.icon_server = QtGui.QIcon(vp.iconfile('server-network'))
        self.icon_memory = QtGui.QIcon(vp.iconfile('memory'))
        self.datasets = []
        self.signal_pick = vaex.events.Signal("pick")
        self.signal_add_dataset = vaex.events.Signal("add dataset")

        self.signal_add_dataset.connect(self.on_add_dataset)
        self.signal_dataset_select = vaex.events.Signal("dataset-select")
        self.currentItemChanged.connect(self.onDatasetSelected)
        # self.items

def __init__(self, thread_pool=None, buffer_size=None, thread_mover=None):
		self.thread_pool = thread_pool or vaex.multithreading.ThreadPoolIndex()
		self.task_queue = []
		self.buffer_size = buffer_size or buffer_size_default
		self.signal_begin = vaex.events.Signal("begin")
		self.signal_progress = vaex.events.Signal("progress")
		self.signal_end = vaex.events.Signal("end")
		self.signal_cancel = vaex.events.Signal("cancel")
		self.thread_mover = thread_mover or (lambda fn, *args, **kwargs: fn(*args, **kwargs))
		self._is_executing = False
		self.lock = threading.Lock()
		self.thread = None

def __init__(self):
        self.signal_begin = vaex.events.Signal("begin")
        self.signal_progress = vaex.events.Signal("progress")
        self.signal_end = vaex.events.Signal("end")
        self.signal_cancel = vaex.events.Signal("cancel")

def __init__(self, ds, **kwargs):
        super(VizBaseState, self).__init__(**kwargs)
        self.ds = ds
        self.signal_slice = vaex.events.Signal()
        self.signal_regrid = vaex.events.Signal()

def __init__(self, thread_pool=None, buffer_size=None, thread_mover=None):
		self.thread_pool = thread_pool or vaex.multithreading.ThreadPoolIndex()
		self.task_queue = []
		self.buffer_size = buffer_size or buffer_size_default
		self.signal_begin = vaex.events.Signal("begin")
		self.signal_progress = vaex.events.Signal("progress")
		self.signal_end = vaex.events.Signal("end")
		self.signal_cancel = vaex.events.Signal("cancel")
		self.thread_mover = thread_mover or (lambda fn, *args, **kwargs: fn(*args, **kwargs))
		self._is_executing = False
		self.lock = threading.Lock()
		self.thread = None

def __init__(self, thread_pool=None, buffer_size=None, thread_mover=None, zigzag=True):
        self.thread_pool = thread_pool or vaex.multithreading.ThreadPoolIndex()
        self.task_queue = []
        self.buffer_size = buffer_size or buffer_size_default
        self.signal_begin = vaex.events.Signal("begin")
        self.signal_progress = vaex.events.Signal("progress")
        self.signal_end = vaex.events.Signal("end")
        self.signal_cancel = vaex.events.Signal("cancel")
        self.thread_mover = thread_mover or (lambda fn, *args, **kwargs: fn(*args, **kwargs))
        self._is_executing = False
        self.lock = threading.Lock()
        self.thread = None
        self.passes = 0  # how many times we passed over the data
        self.zig = True # zig or zag
        self.zigzag = zigzag

def __init__(self):
        self.signal_begin = vaex.events.Signal("begin")
        self.signal_progress = vaex.events.Signal("progress")
        self.signal_end = vaex.events.Signal("end")
        self.signal_cancel = vaex.events.Signal("cancel")