FWIW, the article incorrectly attributes the original idea for the compact dictionary to the PyPy team. That team implemented it based on my research, proposal, and proof-of-concept (see https://mail.python.org/pipermail/python-dev/2012-December/1... and https://morepypy.blogspot.com/2015/01/faster-more-memory-eff... ). At one point, they used to refer to the implementation as the RaymondDict and I rather liked that :-)