pyrsistent is super slow, though. Just ran a quick benchmark:

  - Creation - 8-12x slower  
  - Lookup - 22-27x slower  
  - Contains check - 30-34x slower  
  - Iteration - 5-14x slower  
  - Merge - 32-158x slower  
 

This is rarely the case in practice, most dictionaries and dict operations are small, if you have a huge dict, you probably should be chunking your load or delegating that to infra.

Not to mention pyrsistent's API is incompatible with dicts, so you can't pass it to external code without conversion.

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

> 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.