Python 3 preparation: make fallback SysCallError an actual exception class. The code defines a fallback version of SysCallError when import of OpenSSL.SSL. But in Python 3, defining it as None and then using in "except" statements results in: TypeError: catching classes that do not inherit from BaseException is not allowed

try:
    # Python 3+.
    from xmlrpc import client, server
except ImportError:
    # Python 2.
    import xmlrpclib as client
    import SimpleXMLRPCServer as server