Sandboxed Python: memory limits?

[Chris Angelico]

Is it possible, and if so is it easy, to limit the amount of memory an
embedded Python interpreter is allowed to allocate? I don't want to
ulimit/rlimit the process if I don't have to (or rather, I want the
process's limit to be high, and the Python limit much lower), but just
to force Python to throw MemoryError sooner than it otherwise would
(my code can then graciously deal with the exception).

Google turned up this thread:
http://stackoverflow.com/questions/1760025/limit-python-vm-memory

The answers given include resource.setrlimit (which presumably goes
straight back to the API, which will affect the whole process), and a
simple counter (invasive to the code). But I want something that I can
impose from the outside.

I have a vague memory of reading somewhere that it's possible to
replace the Python memory allocator. This would be an option, if
there's no simple way to say "your maximum is now 16MB", but I now
can't find it back. Was I hallucinating?

Hoping not to reinvent any wheels today!

Thanks!

Chris Angelico