How to add a Callback to Bokeh DataTable?

Question

I am trying to use Bokeh to make an editable DataTable that updates the source data when the data is edited. I started with the standard DataTable example here, and make the editable kwarg to true. Here is where I am at:

from datetime import date
from random import randint

from bokeh.models import ColumnDataSource, Callback
from bokeh.models.widgets import DataTable, DateFormatter, TableColumn
from bokeh.io import output_file, output_notebook, show, vform
output_notebook()
data = dict(dates=[date(2014, 3, i+1) for i in range(10)],
            downloads=[randint(0, 100) for i in range(10)])

source = ColumnDataSource(data)

columns = [TableColumn(field="dates", title="Date", formatter=DateFormatter()),
           TableColumn(field="downloads", title="Downloads")]

callback = Callback(args=dict(Source=source), code="""
       console.log( '#cell edited')""")

data_table = DataTable(source=source, columns=columns, width=400, height=280, editable=True)
data_table.on_change(callback,source)
show(vform(data_table))

This makes an editable data table, but I can't figure out how to get the callback to update the source data, or to configure the source data so that it automatically does that. I thought there was a way to automatically do that with ColumnDataSource, and after trying that tried to write a callback. However it appears the DataTable doesn't have a callback option, but it oddly has an on_change attribute.

Does anyone know how to do this?

Answer 1

Update 2019/07/18. Bokeh v1.0.0 and newer versions

The source data is updated with editable=True and the on_change callback is called when the data attribute is updated. But we need an auxiliar variable to keep the old data source.

from bokeh.models import ColumnDataSource
from bokeh.models.widgets.tables import (
    DataTable, TableColumn, IntEditor
)
from bokeh.io import curdoc
import copy

dict1 = {
    'x': [0, 0, 0, 0, 0, 0],
    'y': [0, 1, 0, 1, 0, 1]
}
source = ColumnDataSource(data=dict1)

old_source = ColumnDataSource(copy.deepcopy(dict1))

columns = [
    TableColumn(field="x", title="x"),
    TableColumn(field="y", title="y", editor=IntEditor(step=1))
]

data_table = DataTable(
    source=source,
    columns=columns,
    width=800,
    editable=True,
    reorderable=False,
)

def on_change_data_source(attr, old, new):
    # old, new and source.data are the same dictionaries
    print('-- SOURCE DATA: {}'.format(source.data))
    print('>> OLD SOURCE: {}'.format(old_source.data))

    # to check changes in the 'y' column:
    indices = list(range(len(old['y'])))
    changes = [(i,j,k) for i,j,k in zip(indices, old_source.data['y'], source.data['y']) if j != k]
    print('>> CHANGES: {}'.format(changes))

    old_source.data = copy.deepcopy(source.data)

print('SOURCE DATA: {}'.format(source.data))

data_table.source.on_change('data', on_change_data_source)

curdoc().add_root(data_table)

Bokeh v0.13.0 and lower versions

This works on Bokeh v0.13.0 and lower versions. :

from bokeh.models import ColumnDataSource
from bokeh.models.widgets import DataTable, TableColumn, HTMLTemplateFormatter
from bokeh.io import curdoc

dict1 = {
    'x':[0]*6,
    'y':[0,1,0,1,0,1]
}
source = ColumnDataSource(data=dict1)

columns = [
    TableColumn(field="x", title="x"),
    TableColumn(field="y", title="y")
]

data_table = DataTable(
    source=source,
    columns=columns,
    width=800,
    editable=True,
)

def on_change_data_source(attr, old, new):
    print('-- OLD DATA: {}'.format(old))
    print('-- NEW DATA: {}'.format(new))
    print('-- SOURCE DATA: {}'.format(source.data))

    # to check changes in the 'y' column:
    indices = list(range(len(old['y'])))
    changes = [(i,j,k) for i,j,k in zip(indices, old['y'], new['y']) if j != k]
    if changes != []:
        for t in changes:  # t = (index, old_val, new_val)
            patch = {
                'y' : [(t[0], int(t[2])), ]   # the new value is received as a string
            }
            # source2.patch(patch)  # to update the values on another source variable for instance

source.on_change('data', on_change_data_source)

curdoc().add_root(data_table)