from bokeh.models import DateRangeSlider, HBox, WidgetBox
from bokeh.io import curdoc

from datetime import datetime

start = '2010-01-01'
end = '2015-01-01'

beginning = DateRangeSlider(
    title="Period:", name="period", value=(start,end),
    bounds=(start,end), range=(dict(days=1), None))

def cb(attr, old, new):
  print(new)

beginning.on_change('value', cb)

curdoc().add_root(HBox(children=[WidgetBox(beginning)]))