on_change_example.py

from bokeh.io import show, curdoc
from bokeh.models.widgets import Button
from bokeh.layouts import row, widgetbox
from bokeh.models import ColumnDataSource, CustomJS
from bokeh import events

button = Button(label = 'Send HelloWorld to console')

source = ColumnDataSource(data=dict())

jscb = CustomJS(code='''
console.log('HelloWorld');
''')

source.js_on_change('data', jscb)

def send_hello_world_to_console():
    source.data = {'data':['str']}
    print 'Confirm that python CB worked'

button.on_click(send_hello_world_to_console)

# Comment this in to make sure that JS code is correct
# button.js_on_event(events.ButtonClick, jscb)

curdoc().add_root(row(widgetbox(button)))