Old Python % string formatting
`%` formatting is a bin-op, and iirc causes a crash because the binop code is expecting modulus, and thus numerical values.

IMO implementing this natively would be crazy.

We should pre-process the input python with tools like https://github.com/ikamensh/flynt to reduce the variability of the input, but that still would need https://github.com/adsharma/py2many/issues/74