Create new tab for tabs

add_tab.py

from bokeh.models.widgets import Panel, Tabs, Button
from bokeh.io import curdoc
from bokeh.plotting import figure
from bokeh.layouts import column, widgetbox

p1 = figure(plot_width=300, plot_height=300)
p1.circle([1, 2, 3, 4, 5], [6, 7, 2, 4, 5], size=20, color="navy", alpha=0.5)
tab1 = Panel(child=p1, title="circle")

p2 = figure(plot_width=300, plot_height=300)
p2.line([1, 2, 3, 4, 5], [6, 7, 2, 4, 5], line_width=3, color="navy", alpha=0.5)
tab2 = Panel(child=p2, title="line")

tabs = Tabs(tabs=[ tab1, tab2 ])
button = Button(label='Add a tab')

def add_a_tab_button_callback():

    p = figure(plot_width=300, plot_height=300)
    p.line([1, 2, 3, 4, 5], [6, 7, 2, 4, 5], line_width=3, color="navy", alpha=0.5)
    t = Panel(child=p, title="line")
    tabs.tabs.append(t)
    print 'OK'

button.on_click(add_a_tab_button_callback)

layout = column([widgetbox(tabs, button)])
curdoc().add_root(layout)

Doesn't seem to work quite right