From the bpython documentation:
pastebin_url
The pastebin url to post to (without a trailing slash). This pastebin has to be a pastebin which uses LodgeIt. Examples are: http://paste.pocoo.org/xmlrpc/ and http://bpaste.net/xmlrpc/ (default: http://bpaste.net/xmlrpc/)
The pocoo.org pastebin is retired, so you can't use that. The default, bpaste.net, is returning a 301 error.
HTTP/1.1 301 Moved Permanently
Date: Tue, 14 Oct 2014 04:56:10 GMT
Content-Type: text/html
Location: https://bpaste.net/xmlrpc/
OK, so update your pastebin_url to use https, right?
HTTP/1.1 404 NOT FOUND
The problem you're having is that bpaste.net is no longer supporting the LodgeIt /xmlrpc/ url. Maybe this is only temporary, or maybe they've retired the public xml interface.
The solution would be to find another LodgeIt pastebin that you can use, or setup your own.
I don't know of any other public LodgeIt pastebins; maybe there are some. A google search turned up this HowTo:
http://killyourtv.i2p.us/howtos/pastebin/