Hmm yes, some more words in the documentation might help.

Does anyone understand why it happens, though?

Specifically, note that

sum(get(i) for i in range(len(l)))

or

eval("get(0) + get(1) + get(2) + get(3)")

or

eval("sum(get(i) for i in range(len(l)))", locals())

work just fine, but

eval("sum(get(i) for i in range(len(l)))")

fails, which is really confusing. I have no mental model of what is happening that allows for the first thing to work, but disallows for the second thing. I understand it has something to do with the creation of a new subscope when the comprehension is run, but other than that, I don't really understand.

Also, ideally, the last thing should work, too.

I am teaching programming to college students and I could not explain to them why the first three worked but the last one failed. There was simply nothing I could say that would give them a good mental model for the execution.