> pyrsistent is super slow, though

Since when is Python about speed?

> Just ran a quick benchmark

Where's the code? Have you observed the bottleneck call?

> Except at 10k+ items, batchup dates on 100K+ items or inserting 100 keys.

> This is rarely the case in practice

Where's the stats on the actual practice?

> You'd better have an incredible ROI to justify that.

The ROI being: fearless API design where 1) multiple instances of high level components are truly independent and could easily parallelize, 2) calling sites know that they keep the original data intact and that callees behave within the immutability constraints, 3) default func inputs and global scope objects are immutable without having to implement another PEP, 4) collections are hashable in general.

Clearly the ROI is perfect for you.

I won't waste more of your time.