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from __future__ import print_function
The ButtonWidget is not 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 doc string of the on_click can be seen below.
from IPython.html import widgets
print(widgets.ButtonWidget.on_click.__doc__)
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.
from IPython.display import display
button = widgets.ButtonWidget(description="Click Me!")
display(button)
def on_button_clicked(b):
print("Button clicked.")
button.on_click(on_button_clicked)
The TextWidget also has a special on_submit event. The on_submit event fires when the user hits return.
text = widgets.TextWidget()
display(text)
def handle_submit(sender):
print(text.value)
text.on_submit(handle_submit)
Widget properties are IPython traitlets and traitlets are eventful. To handle changes, the on_trait_change method of the widget can be used to register a callback. The doc string for on_trait_change can be seen below. Both the name and remove properties are optional.
print(widgets.Widget.on_trait_change.__doc__)
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')
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