El siguiente código no genera un gráfico:

import pandas
import numpy as np
from bokeh.plotting import figure, show, output_file
from bokeh.io import output_notebook
from datetime import datetime

output_notebook()

TOOLS="hover,crosshair,pan,wheel_zoom,zoom_in,zoom_out,box_zoom,undo,redo,reset,\
    tap,save,box_select,poly_select,lasso_select,"

df = pandas.read_csv('./logs.csv')
df['datetime'] = pd.to_datetime(df['datetime'])
xvals = df['datetime'].dt.strftime('%Y-%m-%d')
yvals = df['datetime'].dt.strftime('%H:%M:%S')

p = figure(title="Test Title", width=500, height=500, \
           x_axis_type="datetime", y_axis_type="datetime", \
           x_range=(df.iloc[-1]['datetime'].strftime('%Y/%m/%d'),\
                    df.iloc[0]['datetime'].strftime('%Y/%m/%d')),\
           y_range=('00:00:00','23:59:59'),\
           tools=TOOLS)
p.scatter(xvals, yvals, alpha=0.5)
show(p)

Este gráfico producido es un gráfico en blanco. ¿Cuál es el problema

EDITAR

Actualicé el código con

xvals = df['datetime'].dt.date
yvals = df['datetime'].dt.time

p = figure(title="Activity history", width=800, height=500, \
           x_axis_type='datetime', y_axis_type='datetime',\
           x_axis_label="Date", y_axis_label="Time",\
           tools=TOOLS)

p.scatter(xvals, yvals, alpha=0.3)
show(p)

Y esto produce un gráfico.