The makefile method uses socket_fileobject which doesn't exist.
Most people run roundup behind a real web server apache, nginx etc.
So this is a low priority issue at the moment.

$ python3 roundup/scripts/roundup_server.py -s t=demo
WARNING: generating temporary SSL certificate
Roundup server started on localhost:8080
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 
40976)
Traceback (most recent call last):
  File "/usr/lib/python3.6/socketserver.py", line 620, in 
process_request
    self.finish_request(request, client_address)
  File "/usr/lib/python3.6/socketserver.py", line 364, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python3.6/socketserver.py", line 722, in __init__
    self.setup()
  File "roundup/scripts/roundup_server.py", line 722, in setup
    RoundupRequestHandler.setup(self)
  File "/usr/lib/python3.6/socketserver.py", line 774, in setup
    self.rfile = self.connection.makefile('rb', self.rbufsize)
  File "roundup/scripts/roundup_server.py", line 183, in makefile
    fo = socket._fileobject(self.__conn, mode, bufsize)
AttributeError: module 'socket' has no attribute '_fileobject'
----------------------------------------