How to set interact arguments programmatically?

Question

Suppose I have function, that accepts list of arguments. List can be of variable length and function is ok with it. For example:

import math
import numpy as np
import matplotlib.pyplot as plt
from ipywidgets import interact, interactive, fixed, interact_manual
import ipywidgets as widgets
%matplotlib inline  

def PlotSuperposition(weights):
    def f(x):
        y = 0
        for i, weight in enumerate(weights):
            if i==0:
                y+=weight
            else:
                y += weight*math.sin(x*i)
        return y
    vf = np.vectorize(f)
    xx = np.arange(0,6,0.1)
    plt.plot(xx, vf(xx))
    plt.gca().set_ylim(-5,5)

PlotSuperposition([1,1,2])

shows

I can hardcode interact for given number of arguments, like here

interact(lambda w0, w1, w2: PlotSuperposition([w0,w1,w2]), w0=(-3,+3,0.1), w1=(-3,+3,0.1), w2=(-3,+3,0.1))

which shows

But how can I make number of sliders defined programmatically?

I tried

n_weights=10
weight_sliders = [widgets.FloatSlider(
        value=0,
        min=-10.0,
        max=10.0,
        step=0.1,
        description='w%d' % i,
        disabled=False,
        continuous_update=False,
        orientation='horizontal',
        readout=True,
        readout_format='.1f',
    ) for i in range(n_weights)]
interact(PlotSuperposition, weights=weight_sliders)

but got error

 TypeError: 'FloatSlider' object is not iterable

inside PlotSuperposition saying that interact doesn't pass a list of values to the function.

How to accomplish?

user_444036 · Answer

First, modify your function to take an arbitrary number of keyword arguments instead of a plain list:

def PlotSuperposition(**kwargs):
    def f(x):
        y = 0
        for i, weight in enumerate(kwargs.values()):
            if i==0:
                y+=weight
            else:
                y += weight*math.sin(x*i)
        return y
    vf = np.vectorize(f)
    xx = np.arange(0,6,0.1)
    plt.plot(xx, vf(xx))
    plt.gca().set_ylim(-5,5)

Notice the asterisks in front of kwargs. Then, call interact with a dictionary of key/value arguments:

kwargs = {'w{}'.format(i):slider for i, slider in enumerate(weight_sliders)}

interact(PlotSuperposition, **kwargs)

How to set interact arguments programmatically?

1 Answers