It might be a good idea to import all module once a package is built. It will detect missing dependencies and other errors at build time.

One good reason for such behaviour is that pypy cffi verifier writes some files on first import. If we don't do this during build time, Nix throws permissions errors due to readonly store.

Sample code to get all modules for a package:

import pkgutil
import email

package = email
for importer, modname, ispkg in pkgutil.walk_packages(path=package.__path__,
                                                      prefix=package.__name__+'.',
                                                      onerror=lambda x: None):
    print(modname)