In my code, I had a custom exception declared like this:

class UnknownReleaseError(ValueError): ...

However, when trying to compile this with mypyc, it would yield the following error:

$ mypyc mrtest mrhlpr
mrhlpr/mr.py:177: error: Unsupported statement in class body

I had to change it to this to get it working, which should be functionally identical:

class UnknownReleaseError(ValueError):
    pass

I assume this is unintentional given that it works fine with regular CPython. mypyc version:

$ mypyc --version
mypy 1.11.2 (compiled: yes)