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If we are serious about doing this we will need to audit all the values before/after this PR to make sure they are identical

While I think of it we should also assess the impact on import time of reading all these files

Thanks for the PR! I like the idea, but we need to think a bit more how we implement it. Like @astrofrog, I wonder about the duplication. It might be nice to have a function to look up any constant by name, and get a Constant back. This can then be used in the code to look up the currently defined constants, but allows a user to get any other.

Note that a separate question is whether we are not duplicating too much what scipy does (although it of course does not have the Constant class). Should we vendor their parser? Finally make scipy a required dependency?

Might be good to discuss at the Coordination meeting (astropy/astropy-project#535)? Also xref #12448 for scipy dependency discussion