Python, Bokeh: How to change range of datetime axis

Question

I would like to set the range of a datetime axis using a button. However, the command

f.x_range = Range1d(start=start_date, end=end_date)

doesn't work. When clicking the button nothing happens. I don't get any errors, neither in the terminal windows running the Bokeh server, nor in the console output of my Chrome web browser.

You find the entire code below. I'm grateful for any advice.

Thanks,

Julian

# Import libraries
from bokeh.io import curdoc
from bokeh.models import ColumnDataSource, DatetimeTickFormatter, Select, Range1d
from bokeh.models.widgets import Button
from bokeh.layouts import layout
from bokeh.plotting import figure
from datetime import datetime, timedelta
from math import radians


# Create figure
f=figure(x_axis_type='datetime')

# Create sample datetime data
date_time = [datetime(2017,1,1) + timedelta(days=x) for x in range(0,365)]

# Create ColumnDataSource
source = ColumnDataSource(dict(datetime=date_time,parameter=range(0,365)))

# Create Line
f.line(x='datetime',y='parameter',color='olive',line_color='black',source=source)

# Update xaxis function
def update_xaxis():
    start_date = datetime(year=int(select_start_year.value), month=int(select_start_month.value), day=int(select_start_day.value))
    end_date   = datetime(year=int(select_end_year.value), month=int(select_end_month.value), day=int(select_end_day.value))    
    f.x_range = Range1d(start=start_date, end=end_date)

# Set date format for x axis
f.xaxis.formatter=DatetimeTickFormatter(formats=dict(
    seconds=["%Y-%m-%d %H:%M:%S"],
    minsec=["%Y-%m-%d %H:%M:%S"],
    minutes=["%Y-%m-%d %H:%M:%S"],
    hourmin=["%Y-%m-%d %H:%M:%S"],
    hours=["%Y-%m-%d %H:%M:%S"],
    days=["%Y-%m-%d %H:%M:%S"],
    months=["%Y-%m-%d %H:%M:%S"],
    years=["%Y-%m-%d %H:%M:%S"],
    ))
f.xaxis.major_label_orientation=radians(90)

# Create Select and Button widgets
options=[("2015","2015"),("2016","2016"),("2017","2017")]
select_start_year=Select(title="Start Year",value="2017",options=options)
options=[("01","01"),("02","02"),("03","03"),("04","04"),("05","05"),("06","06"),("07","07"),("08","08"),("09","09"),("10","10"),("11","11"),("12","12")]
select_start_month=Select(title="Start Month",value="01",options=options)
options=[("01","01"),("02","02"),("03","03"),("04","04"),("05","05"),("06","06"),("07","07"),("08","08"),("09","09"),("10","10"),("11","11"),("12","12"),("13","13"),("14","14"),("15","15"),("16","16"),("17","17"),("18","18"),("19","19"),("20","20"),("21","21"),("22","22"),("23","23"),("24","25"),("25","26"),("27","27"),("28","28"),("29","29"),("30","30"),("31","31")]
select_start_day=Select(title="Start Day",value="01",options=options)
options=[("2015","2015"),("2016","2016"),("2017","2017")]
select_end_year=Select(title="End Year",value="2017",options=options)
options=[("01","01"),("02","02"),("03","03"),("04","04"),("05","05"),("06","06"),("07","07"),("08","08"),("09","09"),("10","10"),("11","11"),("12","12")]
select_end_month=Select(title="End Month",value="06",options=options)
options=[("01","01"),("02","02"),("03","03"),("04","04"),("05","05"),("06","06"),("07","07"),("08","08"),("09","09"),("10","10"),("11","11"),("12","12"),("13","13"),("14","14"),("15","15"),("16","16"),("17","17"),("18","18"),("19","19"),("20","20"),("21","21"),("22","22"),("23","23"),("24","25"),("25","26"),("27","27"),("28","28"),("29","29"),("30","30"),("31","31")]
select_end_day=Select(title="End Day",value="01",options=options)
button = Button(label='Set Date')

# Update x axis range on click
button.on_click(update_xaxis)

# Add elements to curdoc 
lay_out=layout([[f],[select_start_year],[select_start_month],[select_start_day],[select_end_year],[select_end_month],[select_end_day],[button]])
curdoc().add_root(lay_out)

Answer 1

I figured out the solution. First off all, I used the Datepicker widget, which is much more elegant than three Select widgets. Then, you have to convert the datetime value from the DatePicker into a float/integer value, which represents the seconds elapsed w.r.t. a reference date, i.e. Jan 1, 1970. Unix calculates this in seconds, Java Script needs this value in milliseconds, hence the multiplication by 1000. Here is the code:

# Import libraries
from bokeh.io import curdoc
from bokeh.models import ColumnDataSource, DatetimeTickFormatter, DatePicker
from bokeh.models.widgets import Button
from bokeh.layouts import layout, column, row
from bokeh.plotting import figure
from datetime import datetime, timedelta
from math import radians


# Create figure
f=figure(x_axis_type='datetime')

# Create sample datetime data
date_time = [datetime(2017,1,1) + timedelta(days=x) for x in range(0,365)]

# Create ColumnDataSource
source = ColumnDataSource(dict(datetime=date_time,parameter=range(0,365)))

# Create Line
f.line(x='datetime',y='parameter',color='olive',line_color='black',source=source)

# Update xaxis function
def update_xaxis():
    # Calculate time delta from reference time in seconds
    timestamp_start = (datetime.combine(datepicker_start.value, datetime.min.time())
                        - datetime(1970, 1, 1)) / timedelta(seconds=1)
    timestamp_end = (datetime.combine(datepicker_end.value, datetime.min.time())
                        - datetime(1970, 1, 1)) / timedelta(seconds=1)
    f.x_range.start = int(timestamp_start)*1e3  # Multiply by 1e3 as JS timestamp is in milliseconds
    f.x_range.end   = int(timestamp_end)*1e3  # Multiply by 1e3 as JS timestamp is in milliseconds

# Set date format for x axis
f.xaxis.formatter=DatetimeTickFormatter(formats=dict(
    seconds=["%Y-%m-%d %H:%M:%S"],
    minsec=["%Y-%m-%d %H:%M:%S"],
    minutes=["%Y-%m-%d %H:%M:%S"],
    hourmin=["%Y-%m-%d %H:%M:%S"],
    hours=["%Y-%m-%d %H:%M:%S"],
    days=["%Y-%m-%d %H:%M:%S"],
    months=["%Y-%m-%d %H:%M:%S"],
    years=["%Y-%m-%d %H:%M:%S"],
    ))
f.xaxis.major_label_orientation=radians(90)

# Create Datepicker and Button widgets
datepicker_start = DatePicker(title='Start Date')
datepicker_end = DatePicker(title='End Date')
button = Button(label='Set Date')

# Update x axis range on click
button.on_click(update_xaxis)

# Add elements to curdoc 
lay_out=layout([[row(f,
                     column(button,
                            row(datepicker_start,datepicker_end)))]])
curdoc().add_root(lay_out)