Do we want to have weakref support?
Here's another thing to consider re: completeness of language implementation: do we want to support weak referenced (weakref module)?
On one hand, it's niche feature used rarely enough. On the other hand, it's something which would pretty much help low-memory usage: ability to cache some object in memory, but safely and transparently free it if there's memory pressure.
But efficient implementation of weakrefs is expensive - each object need to grow to contain pointer to its associated weakref. Taking into account that weakrefs are rare, less runtime-efficient, but much more memory-efficient impl of having a separate mapping from obj to its weakref can be used.
Thoughts/comments are welcome.
weakref: Add basic stub function to aid in porting.
This just allows most basic usages of weakref in other modules to "work" unless they test for actual cleanup via gc.collect etc.
Docs: https://docs.python.org/3/library/weakref.html#weakref.ref