How to have an argument possible values dependent on another argument with IPython Widgets?

Question

Assume I have this simple function in Python:

def f(gender, name):
    if gender == 'male':
        return ranking_male(name)
    else:
        return ranking_female(name)

where gender belongs to ['male', 'female'] whereas name belongs to ['Adam', 'John', 'Max', 'Frodo'] (if gender is male) or ['Mary', 'Sarah', 'Arwen'] (otherwise).

I wish to apply interact from ipywidgets to this function f. Normally one would do

from ipywidgets import interact
interact(f, gender = ('male', 'female'), name = ('Adam', 'John', 'Max', 'Frodo'))

The problem is that the admissible values for name now depend on the value chosen for gender.

I tried to find it in the docs but couldn't find it. The only thing I think may be important is This is used to setup dynamic notifications of trait changes.

    Parameters
    ----------
    handler : callable
        A callable that is called when a trait changes. Its
        signature should be ``handler(change)``, where ``change```is a
        dictionary. The change dictionary at least holds a 'type' key.
        * ``type``: the type of notification.
        Other keys may be passed depending on the value of 'type'. In the
        case where type is 'change', we also have the following keys:
        * ``owner`` : the HasTraits instance
        * ``old`` : the old value of the modified trait attribute
        * ``new`` : the new value of the modified trait attribute
        * ``name`` : the name of the modified trait attribute.
    names : list, str, All
        If names is All, 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.
    type : str, All (default: 'change')
        The type of notification to filter by. If equal to All, then all
        notifications are passed to the observe handler.

But I have no idea how to do it nor to interpret what the doc string is talking about. Any help is much appreciated!

Answer 1

For example you have brand and model of car and model depends on brand.

d = {'Volkswagen' : ['Tiguan', 'Passat', 'Polo', 'Touareg', 'Jetta'], 'Chevrolet' : ['TAHOE', 'CAMARO'] }

brand_widget = Dropdown( options=list(d.keys()),
                         value='Volkswagen',
                         description='Brand:',
                         style=style
                       )
model_widget = Dropdown( options=d['Volkswagen'],
                         value=None,
                         description='Model:',
                         style=style
                       )

def on_update_brand_widget(*args):
    model_widget.options = d[brand_widget.value]

brand_widget.observe(on_update_brand_widget, 'value')