[alecthomas]

> Right, the startling thing about Python's previous dict was that it was so terrible that the ordered dict was actually significantly faster.

I've never heard that before and it would be really surprising, given that Python's builtin dict is used for everything from local symbol to object field lookup. Do you have more information?

[aaronbee]

Here’s a description of the new map implementation and why it’s more efficient: https://www.pypy.org/posts/2015/01/faster-more-memory-effici...

[adgjlsfhk1]

Note that this applies more for python than efficient languages. In python, objects are big, and require an indirection. In faster languages, many objects can be smaller than a pointer and stored inline. As such, dictionaries that have vectorized lookups generally can be made faster.