def ebAuthentication(failure, proto, username, password):
 failure.trap(imap4.NoSupportedAuthentication)
 return proto.prompt('No secure authentication available. Login insecurely? (y/N) ').addCallback(cbInsecureLogin, proto, username, password)

def ebAuthentication ( failure , proto , username , password ) : failure . trap ( imap4 . NoSupportedAuthentication ) return proto . prompt ( 'No secure authentication available. Login insecurely? (y/N) ' ) . addCallback ( cbInsecureLogin , proto , username , password )
errback invoked when authentication fails .