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ipythonjupyter-notebookipywidgets
Little Bobby Tables
Little Bobby Tables

Reputation: 4744

Using Ipython ipywidget to create a variable?

This seems really simple but I have not been able to find a single example or to solve this myself. How do I use an ipywidget widget to create or return a python variable/object, such as a list or string, that can be used in a following cell?

Upvotes: 27

Views: 41737

Answers (3)

Wayne
Wayne

Reputation: 9790

This is to tag onto elz's answer to address ThomasNichols' comments. See my comment here. This code block puts together what I suggest, building on elz's answer:

from ipywidgets import interactive
from IPython.display import display

# Define any function
def f(a, b):
    global the_current_value
    the_current_value = a + b
    display(the_current_value)
    return a + b

# Create sliders using interactive
my_result = interactive(f, a=(1,5), b=(6,10))

# You can also view this in a notebook without using display.
display(my_result)

Others reading this thread may find it useful, and so I'll note I've added an example based on the use of interactive() to have the value selected by a widget get used in realtime, automatic updating in another widget update upon selection under 'Adapting the streamlined version to display the value in a second widget' here.

Asyncio may be the way to go if interactive() not useable

As I pointed out at the bottom of here, this solution to Is it possible to get the current value of a widget slider from a function without using multithreading? might be of interest to those looking for access current values. In that example the use of asyncio there allows to keep getting updated information from a widget that selects a value while allowing use of time.sleep() which seems to block interactive() from working.

Upvotes: 0

harringr
harringr

Reputation: 486

There is a good introduction to ipywidgets at http://blog.dominodatalab.com/interactive-dashboards-in-jupyter/ which answers this question.

You need two widgets, one for input, and another to bind the value of that input. Here's an example for text input:

from ipywidgets import widgets  

# Create text widget for output
output_text = widgets.Text()

# Create text widget for input
input_text = widgets.Text()

# Define function to bind value of the input to the output variable 
def bind_input_to_output(sender):
    output_text.value = input_text.value

# Tell the text input widget to call bind_input_to_output() on submit
input_text.on_submit(bind_input_to_output)

# Display input text box widget for input
input_text

# Display output text box widget (will populate when value submitted in input)
output_text

# Display text value of string in output_text variable
output_text.value

# Define new string variable with value of output_text, do something to it
uppercase_string = output_text.value.upper()
print uppercase_string

You can then use the uppercase_string, or output_text.value string, for example, throughout your notebook.

A similar pattern can be followed for using other input values, e.g. the interact() slider:

from ipywidgets import widgets, interact

# Create text widget for output
output_slider_variable = widgets.Text()

# Define function to bind value of the input to the output variable 
def f(x):
    output_slider_variable.value = str(x)

# Create input slider with default value = 10    
interact(f, x=10)

# Display output variable in text box
output_slider_variable

# Create and output new int variable with value of slider
new_variable = int(output_slider_variable.value)
print new_variable

# Do something with new variable, e.g. cube
new_variable_cubed = pow(new_variable, 3)
print new_variable_cubed

Screenshot of iPython notebook to illustrate binding variables from ipywidgets Text() and interact() for use throughout notebook

Upvotes: 26

elz
elz

Reputation: 5698

Another solution that may be easier is to use interactive. It acts a lot like interact, but allows you access to the returned value in later cells while creating only a single widget.

A simple example is below, and more complete documentation is here

from ipywidgets import interactive
from IPython.display import display

# Define any function
def f(a, b):
    return a + b

# Create sliders using interactive
my_result = interactive(f, a=(1,5), b=(6,10))

# You can also view this in a notebook without using display.
display(my_result)

You can now access the result value, and also the values of the widgets if desired.

my_result.result  # current value of returned object (in this case a+b)
my_result.children[0].value # current value of a
my_result.children[1].value # current value of b

Upvotes: 13

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