I think, much simpler solution is to pin required deps (that may be a conditional pin, only for py2), until we not drop support for py2 as others. No need to reinvent wheel.

+1 for removing setuptools_scm.

I guess I don't know the full context of why one would want setuptools_scm From my perspective, it is a narrowly used package with a very casual attitude towards breaking things upstream ("just upgrade your pip"). I don't use Python 2, but I respect that somewhere between 5-10% of people do for various reasons, and my plan was to keep libraries I maintain installable on Python 2 until the wheels really fall off 😄.

That being said, I dropped sympy from Python 2 installs for this issue, so I no longer have a duck in this race and am I fine with whatever! There was some indications in that thread that pinning setuptools_scm version did not help until pip was upgraded (which happens in current mpmath builds so it's hard to say).

From my perspective, it is a narrowly used package with a very casual attitude towards breaking things upstream ("just upgrade your pip")

Looking on the thread, this seems to be an issue with very old pip versions. The Debian Stretch has something like this.