Python can be compiled without certain modules, including ssl. It's somewhat common for that to happen when users compile Python from source and don't have the libssl headers set up. flask.cli imports ssl unconditionally, but it's only for optional SSL cert support in the dev server, so this can be guarded with except ImportErrror. Werkzeug already has such a workaround, although it's a little more complicated than what needs to be done in Flask.

If no ssl module is imported, using the cert-related options in the CLI should raise a usage error.