What is 'assert self._self_reading_future is None'? (Asyncio)

Question

I am currently trying to run a bokeh server application to do real-time plotting, however I keep getting an assertion error from asyncio that states:

assert self._self_reading_future is None

This occurs not only when I use my own program, but also when I use example programs that others have made, like the one over here. The only place I've managed to find any use of self_reading_future was from asyncio's code on github, yet even after reading through the code I just can't seem to figure out what it means or does. Could someone enlighten me on what I am doing wrong?

EDIT: I'm adding what is printed out in the console when I run the code. Again, the error occurs for whatever program I run, but for the sake of showing some code, here is an example:

from bokeh.layouts import column
from bokeh.models import ColumnDataSource, Slider
from bokeh.plotting import figure
from bokeh.server.server import Server
from bokeh.themes import Theme

from bokeh.sampledata.sea_surface_temperature import sea_surface_temperature

def modify_doc(doc):
    df = sea_surface_temperature.copy()
    source = ColumnDataSource(data=df)

    plot = figure(x_axis_type='datetime', y_range=(0, 25), y_axis_label='Temperature (Celsius)',
                  title="Sea Surface Temperature at 43.18, -70.43")
    plot.line('time', 'temperature', source=source)

    def callback(attr, old, new):
        if new == 0:
            data = df
        else:
            data = df.rolling('{0}D'.format(new)).mean()
        source.data = ColumnDataSource(data=data).data

    slider = Slider(start=0, end=30, value=0, step=1, title="Smoothing by N Days")
    slider.on_change('value', callback)

    doc.add_root(column(slider, plot))

    doc.theme = Theme(filename="theme.yaml")

# Setting num_procs here means we can't touch the IOLoop before now, we must
# let Server handle that. If you need to explicitly handle IOLoops then you
# will need to use the lower level BaseServer class.
server = Server({'/': modify_doc}, num_procs=1)
server.start()

if __name__ == '__main__':
    print('Opening Bokeh application on http://localhost:5006/')

    server.io_loop.add_callback(server.show, "/")
    server.io_loop.start()

and this is what is printed out in the console:

server.io_loop.start()

self.asyncio_loop.run_forever()

File "Location", line 314, in run_forever
assert self._self_reading_future is None

AssertionError

What is 'assert self._self_reading_future is None'? (Asyncio)

0 Answers