The interact function (IPython.html.widgets.interact) automatically creates user interface (UI) controls for exploring code and data interactively. It is the easiest way to get started using IPython's widgets.
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from __future__ import print_function
from IPython.html.widgets import interact, interactive, fixed
from IPython.html import widgets
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 prints its only argument x.
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def f(x):
print(x)
When you pass this function as the first argument to interact along with an integer keyword argument (x=10), a slider is generated and bound to the function.
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interact(f, x=10);
When you move the slider, the function is called and the current value of x is printed.
If you pass True or False, interact will generate a checkbox:
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interact(f, x=True);
If you pass a string, interact will generate a text area.
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interact(f, x='Hi there!');
interact can also be used as a decorator. This allows you to define a function and interact with it in a single shot. As this example shows, interact also works with functions that have multiple arguments.
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@interact(x=True, y=1.0)
def g(x, y):
print(x, y)
Exercise: Interact Basics
There are times when you may want to explore a function using interact, but fix one or more of its arguments to specific values. This can be accomplished by wrapping values with the fixed function.
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def h(p, q):
print(p, q)
When we call interact, we pass fixed(20) for q to hold it fixed at a value of 20.
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interact(h, p=5, q=fixed(20));
Notice that a slider is only produced for p as the value of q is fixed.
When you pass an integer valued keyword argument (x=10) to interact, it generates an integer valued slider control with a range of $[-1\times 10,+3\times10]$. In this case 10 is an abbreviation for an actual slider widget:
IntSlider(min=-10, max=30, step=1, value=10)
In fact, we can get the same result if we pass this IntSlider as the keyword argument for x:
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interact(f, x=widgets.IntSlider(min=-10, max=30, step=1, value=10));
This examples clarifies how interact proceses its keyword arguments:
Widget instance with a value attribute, that widget is used. Any widget with a value attribute can be used, even custom ones.The following table gives an overview of different widget abbreviations:
| Keyword argument | Widget |
|---|---|
True or False |
Checkbox |
'Hi there' |
Text |
value or (min, max) or (min, max, step) if integers are passed |
IntSlider |
value or (min, max) or (min, max, step) if floats are passed |
FloatSlider |
('orange', 'apple') or {'one':1,'two':2} |
Dropdown |
You have seen how the checkbox and textarea widgets work above. Here, more details about the different abbreviations for sliders and dropdowns are given.
If a 2-tuple of integers is passed (min,max) a integer valued slider is produced with those minimum and maximum (inclusive) values. In this case, the default step size of 1 is used.
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interact(f, x=(0,4));
If a 3-tuple of integers is passed (min,max,step) the step size can also be set.
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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).
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interact(f, x=(0.0,10.0));
The step size can be changed by passing a 3rd element in the tuple.
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interact(f, x=(0.01,10.0,0.01));
For both integer and float valued sliders, you can pick the initial value of the widget by passing a default keyword argument to the underlying Python function. Here we set the initial value of a float slider to 5.5.
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@interact(x=(0.0,20.0,0.5))
def h(x=5.5):
print(x)
Dropdown menus can be produced by passing a tuple 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.
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interact(f, x=('apples','oranges'));
If you want a dropdown menu that passes non-string values to the Python function, you can pass a dictionary. The keys in the dictionary are used for the names in the dropdown menu UI and the values are the arguments that are passed to the underlying Python function.
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interact(f, x={'one': 10, 'two': 20});
Exercise: Image Processing
If you are using Python 3, you can also specify widget abbreviations using function annotations. This is a convenient approach allows the widget abbreviations to be defined with a function.
Define a function with an checkbox widget abbreviation for the argument x.
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def f(x:True):
print(x)
Then, because the widget abbreviation has already been defined, you can call interact with a single argument.
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interact(f);
If you are running Python 2, function annotations can be defined using the @annotate function.
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from IPython.utils.py3compat import annotate
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@annotate(x=True)
def f(x):
print(x)
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interact(f);
In addition to interact IPython provides another function, interactive, that is useful when you want to reuse the widget that are produced or access the data that is bound to the UI controls.
Here is a function that returns the sum of its two arguments.
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def f(a, b):
return a+b
Unlike interact, interactive returns a Widget instance rather than immediately displaying the widget.
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w = interactive(f, a=10, b=20)
The widget is a Box, which is a container for other widgets.
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type(w)
The children of the Box are two integer valued sliders produced by the widget abbreviations above.
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w.children
To actually display the widgets, you can use IPython's display function.
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from IPython.display import display
display(w)
At this point, the UI controls work just like they would if interact had been used. You can manipulate them interactively and the function will be called. However, the widget instance returned by interactive also give you access to the current keyword arguments and return value of the underlying Python function.
Here are the current keyword arguments. If you rerun this cell after manipulating the sliders, the values will have changed.
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w.kwargs
Here is the current return value of the function.
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w.result