PyAccu is used only in two places:

• JSON encoder (PyUnicodeWriter is used already for the decoder)
• StringIO (very minimal use of PyAccu)

The newer PyUnicodeWriter seems to be a better tool for aggregating strings and removing PyAccu gets rid of >100 lines of C code while keeping the same functionality.

P.S. The new JSON encoder also performed ~10% better on a completely synthetic test encoding a 20Mb JSON. That JSON in turn was created while investigating the lack of concurrent execution in FastAPI services. Which turned out to be due to JSON encoding.