bpython is still evolving, and in their forums, I can see many such error reports
like these https://bitbucket.org/bobf/bpython/issue/171/bpython-crashes-when-attempting-to-save https://groups.google.com/forum/#!topic/bpython/-3Gq_9ncVZ4 We can hope, as they evolve, these problems will be corrected.
