Comment 1 for bug 1311051

`__pycache__` usage is not limited to Python3 `*.py` files. That directory is used by 'compiled' code of python modules, but is a good place for other similar artifacts. It seems like a great choice for files 'compiled' by cffi – this way multiple Python interpreter versions can use python modules from the same directory. And the system 'site-packages' is not the only place where python modules may be stored.

The problem here is, that there are no cffi-compiled files included for the 'cryptography.hazmat.bindings' module and cffi tries to compile them on runtime. It is good it failed – so we can see the packaging problem.

The 'compiled' extension modules should be included in the 'cryptography.hazmat.bindings' and, maybe, the 'cryptography.hazmat.bindings' should be modified not to try to recompile that.

Here are some hints:
https://cffi.readthedocs.org/en/release-0.8/#distributing-modules-using-cffi