Bokeh Hover Showing ??? instead of Date and Time - python-3.x

Question

I have read lots of questions and answers here and can not seem to fix my issue. I can not get the Hover tool in Bokeh to display the Date and Time correctly, I get ???, I understand this to mean that the Hover cannot read the column in my Dataframe.
I have implemented a lot of fixes and I think what I have here should work.
Here is my code:
This is the code for the data collection:
import cv2 as cv
from datetime import datetime
import pandas as pd
background = None
status_list = [None, None]
times = []
df = pd.DataFrame(columns = ['Start', 'End'])
video = cv.VideoCapture(0, cv.CAP_DSHOW)
while True:
check, frame = video.read()
status = 0
gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
gray = cv.GaussianBlur(gray, (21, 21), 0)
if background is None:
background = gray
continue
delta_frame = cv.absdiff(background, gray)
thresh_delta = cv.threshold(delta_frame, 40, 255, cv.THRESH_BINARY)[1]
thresh_delta = cv.dilate(thresh_delta, None, iterations = 2)
(cnts, _) = cv.findContours(thresh_delta.copy(), cv.RETR_EXTERNAL, cv.CHAIN_APPROX_SIMPLE)
for contour in cnts:
if cv.contourArea(contour) < 2000:
continue
status = 1
(x, y, w, h) = cv.boundingRect(contour)
cv.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 3)
status_list.append(status)
status_list = status_list[-2:]
if status_list[-1] == 1 and status_list[-2] == 0:
times.append(datetime.now())
if status_list[-1] == 0 and status_list[-2] == 1:
times.append(datetime.now())
cv.imshow('Delta', delta_frame)
cv.imshow('Threshold Frame', thresh_delta)
cv.imshow('Colour Frame', frame)
key = cv.waitKey(1)
if key == ord('q'):
if status == 1:
times.append(datetime.now())
break
for i in range(0, len(times), 2):
df = df.append({'Start' :times[i], 'End' :times[i + 1]}, ignore_index = True)
video.release()
cv.destroyAllWindows()
And here is the code for the Bokeh graph:
%run Motion_Detection_Plotting.ipynb
from bokeh.plotting import figure, show, output_file
from bokeh.models import HoverTool, ColumnDataSource, formatters, TickFormatter
df['Start'] = pd.to_datetime(df.Start, format='%Y-%m-%D %H:%M:%S')
df['End'] = pd.to_datetime(df.End, format='%Y-%m-%D %H:%M:%S')
Source=ColumnDataSource(df.Start, df.End)
p = figure(x_axis_type = 'datetime', height = 200, width = 1000, title = 'Motion Graph', sizing_mode = 'stretch_width')
p.yaxis.minor_tick_line_color = None
p.yaxis.major_tick_in = 0
p.xaxis.major_tick_in = 0
p.yaxis.ticker = [0, 1]
p.ygrid.grid_line_color = None
hover = HoverTool(tooltips=[('Start', '#Start{%D/%m %H:%M:%S}'), ('End','#End{%D/%m %H:%M:%S}')],
formatters={'#Start':'datetime', '#End':'datetime'})
p.add_tools(hover)
q = p.quad(left = df['Start'], right = df['End'], bottom = 0, top = 1, color = 'green')
output_file('graph2.html')
show(p)
And here is my outputted graph
Graph with Hover showing ??? instead of date and time

Answer 1

You are very close to a working solution. Your are defining a ColumnDataSource (CDS) but you are not using it and a HoverTool trys to get the needed infromation from the CDS.
Please see the minmal example below with an working Holvertool.
import pandas as pd
from bokeh.plotting import figure, show, output_notebook
from bokeh.models import HoverTool, ColumnDataSource, formatters, TickFormatter
output_notebook()
# dummy data
df = pd.DataFrame({'Start':['2020-01-01 00:00:00'], 'End':['2020-01-01 00:15:00']})
df['Start'] = pd.to_datetime(df.Start, format='%Y-%m-%d %H:%M:%S')
df['End'] = pd.to_datetime(df.End, format='%Y-%m-%d %H:%M:%S')
# bokeh
source=ColumnDataSource(df)
p = figure(x_axis_type = 'datetime')
hover = HoverTool(tooltips=[('Start', '#Start{%D/%m %H:%M:%S}'), ('End','#End{%D/%m %H:%M:%S}')],
formatters={'#Start':'datetime', '#End':'datetime'})
p.add_tools(hover)
# main change is here, data comes from CDS not from DataFrame
q = p.quad(left='Start', right='End', bottom=0, top=1, color='green', source=source)
show(p)
This is the output: