DateRangeSlider error not logged nor shown in CLI

I noticed the following bug: If you have a DateRangeSlider of which max and min are the same date, the browser shows a blank page client side, and the CLI and error loggers don’t show anything unusual.

It took me a while to find the origin of the problem due to the lack of logging.

Conditions hwere this bug was found:

• Tested on both Windows 10 and Ubuntu 16.04
• Python 3.6, tornado 4.5.2, bokeh 0.12.15 (on both systems)
• Firefox (on both systems)

How to reproduce:

• Put this file in a local folder (e.g. softfocus/): https://github.com/hyamanieu/softfocus/blob/master/softfocus/main.py
• change lines 224 to 227 from (after the bug fix)

last_date = self.df['last modification'].max() 
first_date = self.df['last modification'].min()
if last_date == first_date:
    last_date = first_date + timedelta(days=1)

to these two lines:

last_date = self.df['last modification'].max() 
first_date = last_date

With your CLI, cd into the parent folder and execute bokeh serve softfocus --show --log-level debug

Output: blank page on your browser, no errors/warnings in your CLI Expected output: a working webpage with a frozen DateRangeSlider.

[bryevdv]

As an aside, I just checked and Ion range slider still does not support vertical orientations which is a shame. I would switch to it in a heartbeat except for that deficiency. I’m almost to the point of considering it anyway. If people need vertical sliders that could be the custom extension.

[bryevdv]

@hyamanieu Sorry when you said “same date” I assume you meant same day but different times. If you mean the exact same date, then it would appear the underlying slider library does not support start and end being equal, which is outside our control. As @mattpap says we can try to add better code to disallow that or at least throw better errors. If this is a capability you need, you can consider extending Bokeh with a custom extension for a different slider library. The is an example of wrapping the Ion range slider here, for instance:

https://bokeh.pydata.org/en/latest/docs/user_guide/extensions_gallery/widget.html