To reproduce the problem, apply the nomemory_allocator.patch from issue 30695 and run the following two statements that must be interrupted with ^C:
$  ./python -q
>>> import _testcapi
>>> _testcapi.set_nomemory_allocator()
sys.excepthook is missing
^Cpython: Objects/call.c:785: PyEval_CallObjectWithKeywords: Assertion `!PyErr_Occurred()' failed.
Aborted (core dumped)

The attached patch fixes this problem.
No PR for the moment: this patch and nomemory_allocator.patch are needed to demonstrate other issues.

The patch is far too simplistic. With this patch an exception kills the interactive loop, for example:

$ ./python -q
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
$

See also my old issue #8070 opened 7 years ago :-)

New changeset e0582a37c8d1776a2fd4968e9216f3a05f780276 by xdegaye in branch 'master':
bpo-30696: Fix the REPL looping endlessly when no memory (GH-4160)
https://github.com/python/cpython/commit/e0582a37c8d1776a2fd4968e9216f3a05f780276

New changeset ea5b545e38b3fec7ff29276b5cd59dec583ebf34 by xdegaye in branch '3.6':
[3.6] bpo-30696: Fix the REPL looping endlessly when no memory (GH-4160). (#4379)
https://github.com/python/cpython/commit/ea5b545e38b3fec7ff29276b5cd59dec583ebf34

Thanks for fixing this very old bug!

What about Python 2.7?

> What about Python 2.7?

_testcapi.set_nomemory() does not exist on Pyhton 2.7 so the changes cannot be tested. Applying the changes to PyRun_InteractiveLoopFlags() in 2.7 looks rather straightforward but there are too many differences in PyRun_InteractiveOneFlags() between 2.7 and 3.7.

Also the existing test coverage of these functions in all the Python versions is very weak.

Ok, I understand, thanks for the explanation.