In an empty dir, e.g. Desktop, the following import raises SystemError:

>>> from . import foo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: Parent module '' not loaded, cannot perform relative import

The documentation says that SystemError should be reported as a bug.

You are correct that SystemError indicates a non-fatal issue in the interpreter and thanks for reporting the matter.  In this case I'd say that SystemError is the wrong exception type.  I expect that ImportError (or perhaps RuntimeError) is more appropriate.  However, Brett will have a better idea of why we raise SystemError instead.

It's that way because that's how import.c has it coded in Python 2.7: https://hg.python.org/cpython/file/309cbbc32491/Python/import.c#l2462 . Here is how it looks in Python 2:

%%python2
from __future__ import absolute_import
from . import foo
-----------------------------------------------------
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ValueError: Attempted relative import in non-package


I think another sanity check needs to be added to https://github.com/python/cpython/blob/829b49cbd2e4b1d573470da79ca844b730120f3d/Lib/importlib/_bootstrap.py#L919 for when __package__ is None but level > 0 and then raise the ValueError like in Python 2.

Linking this issue with #18018 - same problem, same situation.