Changing options of Select widget triggers Callback

@jasongrout we should have a way to change the options of a Select widget without triggering the callback function. Whenever the options are changed for the widget the value attribute is automatically set which forces the callback to be triggered. See code below;

from ipywidgets import Select

# callback
def cb(change):
    print(change)

# widget
s_w = Select(value=None, options=['a','b'])
s_w.observe(cb, names='value')

# triggers no callback
s_w.value = None
# triggers callback
s_w.options = ['1', '2', '3']

[nickpollari]

@crahan my workaround has been to utilize the .unobserve method before updating the options.

s_w.unobserve(cb, 'value')
s_w.options = ['1','2','3']
s_w.observe(cb, 'value')

[martinRenou]

Should fix #3284