@nlewo, thanks for your PR! By analyzing the history of the files in this pull request, we identified @FRidh to be a potential reviewer.

Dependency of #25752.

Since the latest version of pythonPackages.pyelasticsearch requires
pythonPackages.elasticsearch < 2, we preserve the old version.

The last pyelasticsearch update we got is one and a half year ago and the package is hardly seeing any maintenance, so I think its better to just remove the expression.

@dtulig , you originally added the expression.

If you're updating a whole stack of packages that belong together, then please bundle them as separate commits in a single PR.

One consideration to keep in mind before removing it is the python elastic search library tracks the elastic search versions. It would be reasonable to keep the latest pyelasticsearch_1, pyelasticsearch_2, pyelasticsearch_5 available, with a default, pyelasticsearch, on the most recent stable elasticsearch version (in this case, that appears to be 5) or the primary nixpkgs supported elasticsearch (perhaps 2.x?). Nixpkgs has elasticsearch for 1.x and elasticsearch2 for 2.x.

That said, I'm not attached to keeping 1.x around so if others feel strongly about keeping a single version I'm ok with that.