When I discovered str(b'bytes') in my Python 3 program was causing errors to be serialized to disk, I was unhappy. It turns out there is a command line option to turn it off, but the vulnerable serialization code is not going to be able to set that argument; or the one-argument-per-shebang limit we have in Linux was already used for something else.

Instead, provide a threadlocal variable that causes str(bytes) to raise. A context manager makes it simple to use for just a portion of your code:

with string.StrBytesRaises():
   no_str_bytes_here()

If not set or False then Python behaves as before.