fwiw this sort of thing may be reasonable to backport to 3.9 as it is more than just a performance enhancement but also a resource consumption bug and should result in no behavior change.

"""
In case of form contain very large data ( in my case the string to parse was about 6000000 byte )
Old code use list of bytes during parsing consumes a lot of memory
New code will use bytearry , which use less memory
""" - text from the original PR