@skosukhin Local imports are usually done to optimize on startup time. Here though I don't understand what's going on, since the two forms seem to me semantically equivalent:

import foo
s = foo.func()

vs.

import foo as bar
s = bar.func()

Can you be more explicit what is the issue and why this is solving it?

First, in the scenarios that I've checked, spack.concretize is already imported by this time. Therefore, we don't seem to get any startup time optimization here.

Second, import without as assigns the module to variable spack, which makes spack an unassigned local variable when we raise spack.error.SpecError() a little earlier in the code. We could also add global spack at the beginning of the method or perform the local import before raising the error.

@skosukhin Thanks. TIL this gotcha, that a nested import as the effect of assigning to the root module. Will search for references in Python docs to read more about that.

We could also add global spack at the beginning of the method or perform the local import before raising the error.

I would be for performing the local import at the beginning of the function. Can you add a test to check that we raise the correct exception (i.e. SpecError and not UnboundLocalError)?

Thanks!