from __future__ import print_function # 2.7 compatability from IPython.html import widgets # Widget definitions from IPython.display import display # Used to display widgets in the notebook
As mentioned in Part 1, the widget attributes are IPython traitlets. Traitlets are eventful. To handle changes, the
on_trait_change method of the widget can be used to register a callback. The docstring for
on_trait_change can be seen below. Both the
remove properties are optional.
Setup a handler to be called when a trait changes. This is used to setup dynamic notifications of trait changes. Static handlers can be created by creating methods on a HasTraits subclass with the naming convention '_[traitname]_changed'. Thus, to create static handler for the trait 'a', create the method _a_changed(self, name, old, new) (fewer arguments can be used, see below). Parameters ---------- handler : callable A callable that is called when a trait changes. Its signature can be handler(), handler(name), handler(name, new) or handler(name, old, new). name : list, str, None If None, the handler will apply to all traits. If a list of str, handler will apply to all names in the list. If a str, the handler will apply just to that name. remove : bool If False (the default), then install the handler. If True then unintall it.
Mentioned in the doc string, the callback registered can have 4 possible signatures:
Using this method, an example of how to output an IntSliderWiget's value as it is changed can be seen below.
int_range = widgets.IntSliderWidget() display(int_range) def on_value_change(name, value): print(value) int_range.on_trait_change(on_value_change, 'value')
ButtonWidget is a special widget, like the
TabWidget, that isn't used to represent a data type. Instead the button widget is used to handle mouse clicks. The
on_click method of the
ButtonWidget can be used to register function to be called when the button is clicked. The docstring of the
on_click can be seen below.
Register a callback to execute when the button is clicked. The callback will be called with one argument, the clicked button widget instance. Parameters ---------- remove : bool (optional) Set to true to remove the callback from the list of callbacks.
Button clicks are transmitted from the front-end to the back-end using custom messages. By using the
on_click method, a button that prints a message when it has been clicked is shown below.
button = widgets.ButtonWidget(description="Click Me!") display(button) def on_button_clicked(b): print("Button clicked.") button.on_click(on_button_clicked)
Button clicked. Button clicked. Button clicked.
Event handlers can also be used to create widgets. In the example below, clicking a button spawns another button with a description equal to how many times the parent button had been clicked at the time.
def new_button(clicked): button = widgets.ButtonWidget() button.clicks = 0 clicked.clicks += 1 button.description = "%d" % clicked.clicks display(button) button.on_click(new_button) button = widgets.ButtonWidget(description = "Start") button.clicks = 0 display(button) button.on_click(new_button)