Infinite exception loop in asyncio coroutine mode on exit() or quit()

[brownan]

If you run the async example from here: https://github.com/prompt-toolkit/ptpython/blob/master/examples/asyncio-python-embed.py

and execute a exit() or quit() statement, the prompt goes into an infinite loop of errors that look like this:

Traceback (most recent call last):
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/application/application.py", line 955, in run
    loop = asyncio.get_event_loop()
  File "/usr/lib/python3.9/asyncio/events.py", line 642, in get_event_loop
    raise RuntimeError('There is no current event loop in thread %r.'
RuntimeError: There is no current event loop in thread 'Thread-178'.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/tmp/venv/lib/python3.9/site-packages/ptpython/repl.py", line 202, in run_async
    text = await loop.run_in_executor(None, self.read)
  File "/usr/lib/python3.9/concurrent/futures/thread.py", line 52, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/tmp/venv/lib/python3.9/site-packages/ptpython/python_input.py", line 1095, in read
    result = self.app.run(pre_run=pre_run, in_thread=True)
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/application/application.py", line 943, in run
    raise exception
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/application/application.py", line 929, in run_in_thread
    result = self.run(
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/application/application.py", line 958, in run
    return asyncio.run(coro)
  File "/usr/lib/python3.9/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
    return future.result()
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/application/application.py", line 875, in run_async
    return await _run_async(f)
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/application/application.py", line 728, in _run_async
    with self.input.raw_mode(), self.input.attach(
  File "/tmp/venv/lib/python3.9/site-packages/prompt_toolkit/input/vt100.py", line 134, in raw_mode
    return raw_mode(self.stdin.fileno())
ValueError: I/O operation on closed file

I have to Ctrl-Z to pause the process or kill it from another window, since Ctrl-C is not effective at this point.

The thread ID in the exception message increases, so I gather it's continuously spawning threads which each crash since stdin has been closed by exit()

This is on Ubuntu linux 20.04 with Python 3.9

[brownan]

Did some digging. In the repl.py function run_and_show_expression_async() a SystemExit is handled by returning.

ptpython/ptpython/repl.py

Lines 156 to 176 in 91d2c35

	async def run_and_show_expression_async(self, text: str):
	loop = asyncio.get_event_loop()
	try:
	result = await self.eval_async(text)
	except KeyboardInterrupt: # KeyboardInterrupt doesn't inherit from Exception.
	raise
	except SystemExit:
	return
	except BaseException as e:
	self._handle_exception(e)
	else:
	# Print.
	if result is not None:
	await loop.run_in_executor(None, lambda: self.show_result(result))
	# Loop.
	self.current_statement_index += 1
	self.signatures = []
	# Return the result for future consumers.
	return result

This swallows the exception and causes the calling code in run_async() to proceed to its next iteration. Calling in to read a new line of input gets the error about I/O operation on closed file.

The sync version, however, re-raises a SystemExit:

ptpython/ptpython/repl.py

Lines 96 to 115 in 91d2c35

	def run_and_show_expression(self, expression: str) -> None:
	try:
	# Eval.
	try:
	result = self.eval(expression)
	except KeyboardInterrupt:
	# KeyboardInterrupt doesn't inherit from Exception.
	raise
	except SystemExit:
	raise
	except BaseException as e:
	self._handle_exception(e)
	else:
	# Print.
	if result is not None:
	self.show_result(result)
	# Loop.
	self.current_statement_index += 1
	self.signatures = []

Is there any reason for the async version to not also do the same?

These two commits are related:
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78c5a0d