attempt to save csv of selection from bokeh plot (not working)

save_selection.py

"""Run this example as: python save_selection.py

Then navigate to localhost:5000

Use python save_selection.py -h for more options.
"""
import base64

import pandas as pd
import numpy as np

from bokeh.server.server import Server
from bokeh.application import Application
from bokeh.application.handlers.function import FunctionHandler
from bokeh.plotting import figure
from bokeh.layouts import layout
from bokeh.models import ColumnDataSource, CustomJS
from bokeh.models.widgets import Button


def scatterplot(source):
    tools = ['pan', 'box_select', 'wheel_zoom', 'reset']
    scatter = figure(title='scatterplot', tools=tools,
                     active_drag='box_select')
    scatter.circle(source=source, x='x', y='y')
    return scatter


def save_selected(dataframe, selection):
    data = dataframe.iloc[selection]
    print(f'I got your df right here! {data.shape}')
    csv = data.to_csv()
    b64 = base64.b64encode(csv.encode()).decode()  # str -> bytes -> b64 -> str
    jscode = f"""
        var link = document.createElement("a");
        link.href = "data:text/csv;base64,{b64}";
        link.download = "selected_data.csv";
        link.target = "_blank";
        link.style.visibility = "hidden";
        console.log("saving selected data:");
        console.log("{b64}");
        link.dispatchEvent(new MouseEvent("click"));
    """
    print('b64 encoded: ', b64)
    return CustomJS(code=jscode)


def generate_makedoc_function(dataframe):
    def makedoc(doc):
        source = ColumnDataSource(dataframe)
        scatter = scatterplot(source)
        savebutton = Button(label='download selected points')
        savebutton.js_on_click(save_selected(dataframe, selection=[]))

        def update_selection(attr, old, new):
            # js_on_click appends a callback, but we want to replace it.
            # so, we clear first.
            savebutton.js_property_callbacks.clear()
            new_js_callback = save_selected(dataframe, selection=new.indices)
            savebutton.js_on_click(new_js_callback)

        source.on_change('selected', update_selection)
        page_content = layout([[scatter], [savebutton]])
        doc.title = 'save selected points!'
        doc.add_root(page_content)
    return makedoc


def main(path='/', port=5000):
    df = pd.DataFrame({'x': np.random.random(100),
                       'y': np.random.random(100),
                       'useful': np.random.randint(0, 100, size=100)})
    apps = {path: Application(FunctionHandler(generate_makedoc_function(df)))}
    server = Server(apps, port=port, allow_websocket_origin=['*'])
    server.run_until_shutdown()


if __name__ == '__main__':
    main()