interact_abbreviations.md

Use abbreviations to generate widgets

This guide addresses how to use abbreviations to create widgets with Panel interact.

1. The [How to > Generate Widgets for Function Arguments](interact_basics) guide provides an overview of how to generate widgets for function arguments with Panel interact.

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At the most basic level, interact autogenerates UI controls for function arguments, and then calls the function with those arguments when you manipulate the controls interactively.

To use interact, you need to define a function that you want to explore. Here is a function that return its argument.

import panel as pn
from panel.interact import interact
from panel import widgets

pn.extension() # for notebook

def f(x):
    return x

When you pass this function to interact along with x=10, a slider is generated and bound to the function parameter, such that when you interact with the widget, the function is called.

interact(f, x=10)

When you pass an integer-valued keyword argument of 10 (x=10) to interact, it generates an integer-valued slider control with a range of [-10,+3*10]. In this case, 10 is an abbreviation for an actual slider widget:

slider_widget = widgets.IntSlider(start=-10,end=30,step=1,value=10)

In fact, we can get the same result if we pass this IntSlider as the keyword argument for x:

interact(f, x=slider_widget)

This examples clarifies how interact processes its keyword arguments:

1. If the keyword argument is a Widget instance with a value attribute, that widget is used. Any widget with a value attribute can be used, even custom ones.

2. Otherwise, the value is treated as a widget abbreviation that is converted to a widget before it is used.

The following table gives an overview of different widget abbreviations:

Keyword argument	Widget
True or False	Checkbox
'Hi there'	Text
value or (min,max,[step,[value]]) if integers are passed	IntSlider
value or (min,max,[step,[value]]) if floats are passed	FloatSlider
['orange','apple'] or {'one':1,'two':2}	Dropdown

Note that a dropdown is used if a list or a dict is given (signifying discrete choices), and a slider is used if a tuple is given (signifying a range).

You have seen how the IntSlider widget works above. Here, more details about the different abbreviations for sliders and dropdowns are given.

If a 2-tuple of integers is passed (min,max), an integer-valued slider is produced with those minimum and maximum values (inclusively). In this case, the default step size of 1 is used.

interact(f, x=(0, 4))

If a 3-tuple of integers is passed (min,max,step), the step size can also be set.

interact(f, x=(0, 8, 2))

A float-valued slider is produced if the elements of the tuples are floats. Here the minimum is 0.0, the maximum is 10.0 and step size is 0.1 (the default).

interact(f, x=(0.0, 10.0))

The step size can be changed by passing a third element in the tuple.

interact(f, x=(0.0, 10.0, 0.01))

For both integer and float-valued sliders, you can pick the initial value of the widget by supplying a default keyword argument when you define the underlying Python function. Here we set the initial value of a float slider to 5.5.

@interact(x=(0.0, 20.0, 0.5))
def h(x=5.5):
    return x

h

You can also set the initial value by passing a fourth element in the tuple.

interact(f, x=(0.0, 20.0, 0.5, 5.5))

Use None as the third element to just set min, max, and value.

interact(f, x=(0.0, 20.0, None, 5.5))

Dropdown menus are constructed by passing a list of strings. In this case, the strings are both used as the names in the dropdown menu UI and passed to the underlying Python function.

interact(f, x=['apples', 'oranges'])

When working with numeric data interact will automatically add a discrete slider:

interact(f, x=dict([('one', 10), ('two', 20)]))

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