Fixed python3 'lod' bug

[philippjfr]

Fix for #1005. Still don't know what actually caught the bug as 'lod' should always be available in the defaults but this will fix the immediate issue.

[philippjfr]

Ready to merge when tests pass.

[jlstevens]

I remember suggesting this as a temporary fix and I am happy to merge. I'm just wondering what we can do to try and address the underlying issue?

[philippjfr]

I'm just wondering what we can do to try and address the underlying issue?

Add a bunch of print statements to Parameterized.defaults, spawn 50 python3 processes which each instantiate a bokeh ElementPlot and call defaults on it, would be my only suggestion.

[jlstevens]

Sounds like a real pain!

It isn't something we need to do now but maybe we should still have an issue to remind us that it is still an issue? What bad behavior can we expect when the lod is missing after this fix?

[philippjfr]

What bad behavior can we expect when the lod is missing after this fix?

Unless someone sets an explicit lod configuration as a plot option it will make zero difference. If they do and this bug occurs then it will fall back to the lod defaults bokeh sets up for all the options the user didn't define.

[jlstevens]

Ok. Doesn't sound too bad, but it is probably worth filing an issue just to register that we are aware of this issue.

Merging.