Events

Events are a mechanism to send notifications. HyperSpy events are decentralised, meaning that there is not a central events dispatcher. Instead, each object that can emit events has an events attribute that is an instance of Events and that contains instances of Event as attributes. When triggered the first keyword argument, obj contains the object that the events belongs to. Different events may be triggered by other keyword arguments too.

Connecting to events

The following example shows how to connect to the index_changed event of DataAxis that is triggered with obj and index keywords:

>>> s = hs.signals.Signal1D(np.random.random((10,100)))
>>> nav_axis = s.axes_manager.navigation_axes[0]
>>> nav_axis.name = "x"
>>> def on_index_changed(obj, index):
...    print("on_index_changed_called")
...    print("Axis name: ", obj.name)
...    print("Index: ", index)

>>> nav_axis.events.index_changed.connect(on_index_changed)
>>> s.axes_manager.indices = (3,)
on_index_changed_called
Axis name: x
Index: 3
>>> s.axes_manager.indices = (9,)
on_index_changed_called
Axis name: x
Index: 9

It is possible to select the keyword arguments that are passed to the connected. For example, in the following only the index keyword argument is passed to on_index_changed2 and none to on_index_changed3:

>>> def on_index_changed2(index):
...    print("on_index_changed2_called")
...    print("Index: ", index)

>>> nav_axis.events.index_changed.connect(on_index_changed2, ["index"])
>>> s.axes_manager.indices = (0,)
on_index_changed_called
Axis name: x
Index: 0
on_index_changed2_called
Index: 0
>>> def on_index_changed3():
...    print("on_index_changed3_called")

>>> nav_axis.events.index_changed.connect(on_index_changed3, [])
>>> s.axes_manager.indices = (1,)
on_index_changed_called
Axis name: x
Index: 1
on_index_changed2_called
Index: 1
on_index_changed3_called

It is also possible to map trigger keyword arguments to connected function keyword arguments as follows:

>>> def on_index_changed4(arg):
...    print("on_index_changed4_called")
...    print("Index: ", arg)

>>> nav_axis.events.index_changed.connect(on_index_changed4, {"index" : "arg"})
>>> s.axes_manager.indices = (4,)
on_index_changed_called
Axis name: x
Index: 4
on_index_changed2_called
Index: 4
on_index_changed3_called
on_index_changed4_called
Index: 4

Suppressing events

The following example shows how to suppress single callbacks, all callbacks of a given event and all callbacks of all events of an object.

>>> with nav_axis.events.index_changed.suppress_callback(on_index_changed2):
...    s.axes_manager.indices = (7,)
on_index_changed_called
Axis name: x
Index: 7
on_index_changed3_called
on_index_changed4_called
Index: 7
>>> with nav_axis.events.index_changed.suppress():
...    s.axes_manager.indices = (6,)

>>> with nav_axis.events.suppress():
...    s.axes_manager.indices = (5,)

Triggering events

Although usually there is no need to trigger events manually, there are cases where it is required. When triggering events manually it is important to pass the right keywords as specified in the event docstring. In the following example we change the data attribute of a BaseSignal manually and we then trigger the data_changed event.

>>> s = hs.signals.Signal1D(np.random.random((10,100)))
>>> s.data[:] = 0
>>> s.events.data_changed.trigger(obj=s)