Python callback in Bokeh issue

Question

I am trying to get a callback function to work in bokeh based on this simple example:

from bokeh.plotting import figure, curdoc
from bokeh.layouts import column
from bokeh.models import ColumnDataSource

TOOLS = "tap,reset"
p = figure(title="Some Figure", tools=TOOLS)

source = ColumnDataSource(dict(x=[[1, 3, 2], [3, 4, 6, 6]],
                y=[[2, 1, 4], [4, 7, 8, 5]], name=['A', 'B']))

pglyph = p.patches('x', 'y', source=source)

def callback(attr, old, new):
    # The index of the selected glyph is : new['1d']['indices'][0]
    print("In callback")
    patch_name =  source.data['name'][new['1d']['indices'][0]]
    print("TapTool callback executed on Patch {}".format(patch_name))

pglyph.data_source.on_change('selected',callback)

curdoc().add_root(column(p))

When I load the page and click on a polygon, I do not see the callback getting executed.

What is missing?

Eugene Pakhomov · Accepted Answer · 2020-07-18 17:34:51Z

4

That's because the selected attribute value is not changed. The contained object is changed instead, and Bokeh doesn't detect deep changes.

Try replacing the callback function and the next line with:

def callback(attr, old, new):
    print("In callback")
    patch_name = source.data['name'][new[0]]
    print("TapTool callback executed on Patch {}".format(patch_name))


pglyph.data_source.selected.on_change('indices', callback)

answered Jul 18, 2020 at 17:34

Eugene Pakhomov

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