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Doing one of the following crashes Python.
 del __builtins__
 a{Tab}
or
 builtins = __builtins__
 del __builtins__
 a{Tab}
If you do a print screen, immediately, you will see the following error:
 *** Internal Error: rpc.py:SocketIO.localcall()
 Object: exec
 Method: <bound method Executive.get_the_completion_list of <idlelib.run.Executive object at 0x0000000002DC2710>>
 Args: ('', 1)
 Traceback (most recent call last):
 File "C:\Python32\lib\idlelib\rpc.py", line 188, in localcall
 ret = method(*args, **kwargs)
 File "C:\Python32\lib\idlelib\run.py", line 327, in get_the_completion_list
 return self.autocomplete.fetch_completions(what, mode)
 File "C:\Python32\lib\idlelib\AutoComplete.py", line 189, in fetch_completions
 namespace.update(__main__.__builtins__.__dict__)
AttributeError: 'module' object has no attribute '__builtins__'
Additionally, when __builtins__ is deleted (in IDLE), __builtins__ becomes a dictionary. If one were to then do __builtins__.clear(), the interpreter stops all interpreting. IDLE moreorless becomes a text editor with syntax highlighting. If you try to use autocomplete, Python hangs before crashing.
I realize that doing such is pointless, but it behaves differently than interactive console interpreters. Interactive console interpreters don't convert __builtins__ to a dictionary upon its deletion. I feel that this error can be handled to prevent crashing.

This is the same as issue 15113. If you delete __builtins__, don't expect Python to work.