In 3.6 just setting the recursion level to 20 produces following output on terminal:

----------------------------------------
Unhandled server exception!
Thread: SockThread
Client Address:  ('127.0.0.1', 41515)
Unhandled exception in thread started by 

and a hang.

In 2.7 it produces:

----------------------------------------
Unhandled server exception!
Thread: SockThread
Client Address:  ('127.0.0.1', 35043)
Request:  <socket._socketobject object at 0xb70e4a84>
Traceback (most recent call last):
  File "/home/serhiy/py/cpython-2.7-debug/Lib/SocketServer.py", line 290, in _handle_request_noblock
    self.process_request(request, client_address)
  File "/home/serhiy/py/cpython-2.7-debug/Lib/SocketServer.py", line 318, in process_request
    self.finish_request(request, client_address)
  File "/home/serhiy/py/cpython-2.7-debug/Lib/SocketServer.py", line 331, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/home/serhiy/py/cpython-2.7-debug/Lib/idlelib/rpc.py", line 500, in __init__
    SocketServer.BaseRequestHandler.__init__(self, sock, addr, svr)
  File "/home/serhiy/py/cpython-2.7-debug/Lib/SocketServer.py", line 652, in __init__
    self.handle()
  File "/home/serhiy/py/cpython-2.7-debug/Lib/idlelib/run.py", line 292, in handle
    rpc.RPCHandler.getresponse(self, myseq=None, wait=0.05)
  File "/home/serhiy/py/cpython-2.7-debug/Lib/idlelib/rpc.py", line 280, in getresponse
    response = self._getresponse(myseq, wait)
  File "/home/serhiy/py/cpython-2.7-debug/Lib/idlelib/rpc.py", line 300, in _getresponse
    response = self.pollresponse(myseq, wait)
RuntimeError: maximum recursion depth exceeded

*** Unrecoverable, server exiting!
----------------------------------------

and restarts the shell.

Definitely the 20 limit is too low for IDLE.