Expose NoSectionError at package level

[honnix]

Description

Expose NoSectionError at package level so that from luigi.configuration import NoSectionError would work.

Motivation and Context

It used to work like this until #2457, so we should probably bring it back for backward compatibility.

Have you tested this? If so, how?

TBD

[ulzha]

+1

I guess the reason we "should probably" is just so that we keep compatibility?

The whole idea of using NoSectionError exception as a way for checking if a section exists, seems like abuse of exceptions.

[honnix]

Yeah the reason is to keep backward compatibility. It is indeed a bad idea to abuse exception. Maybe we should instead let it break in this case.

[honnix]

@Tarrasch @dlstadther wdyt?

[dlstadther]

Am i correct that NoSectionError is just coming from configparser/ConfigParser? Other places in Luigi which need that just reimport from config parser. So i'd say no need to keep in package init

[honnix]

You are right it is from ConfigParse. The problem is not Luigi itself but user code because they could access from init, and now that breaks. The risk is low and very easy to fix by users themselves if we ever get complaints.

[dlstadther]

Yeah, i'm fine letting that break. At some point, we need to drop support for certain things. This is a small case for that.

[honnix]

👍 Let's go for it.