> With data as (b"a" * _4G) the result is as expected:
>
>     Traceback (most recent call last):
>       File "pickle-bigmem-test.py", line 5, in <module>
>         out = dumps(data)
>     OverflowError: cannot serialize a string larger than 4GB
>
> But with (b"a" * _2G), I get this:
>
>     Traceback (most recent call last):
>       File "pickle-bigmem-test.py", line 7, in <module>
>         result = loads(out)
>     _pickle.UnpicklingError: BINUNICODE pickle has negative byte count

Correction: these should be ("a" * _4G) and ("a" * _2G).