Support overriding DEFAULT_INDEXES

[koterpillar]

Setting elasticutils.DEFAULT_INDEXES does nothing due to the fact that the default value is recorded as None on the compile stage. Besides, putting a (potentially) mutable value as a default is bad practice.

[willkg]

You're right in that argument defaults shouldn't be mutable, but that's not the case here--it's None. DEFAULT_INDEXES isn't intended to be overridden--you should instead subclass S and provide your own get_indexes() implementation.

Generally, changing module-level properties is a bad idea since they get set at module load time.

Unless you have a really compelling reason to do what you're trying to do instead of subclassing S and overriding get_indexes(), I'm going to close this PR because this isn't really what we want to be doing.

[koterpillar]

In many project, module-level properties are actually configuration, I thought that was the case here (especially after successfully overriding DEFAULT_URL). Shouldn't this constant be removed altogether then, not to give a misleading impression?

[willkg]

I don't think I know of any projects that have module-level configuration like this where you change things after the module has been loaded. Usually you have to create your own configuration file like settings.py in Django. That's different.

That constant isn't documented anywhere, so I don't consider it part of the API. I don't think I want to add this to the API--these are really intended to be internal only. Ergo, I'll add a comment that says, "Don't change these, please." I think that covers this and the other constants in that module which are all in a similar situation.

Thank you!

[koterpillar]

Thanks for the explanation!