Bug report

Checklist

• I am confident this is a bug in CPython, not a bug in a third-party project
• I have searched the CPython issue tracker,
  and am confident this bug has not been reported before

CPython versions tested on:

3.8, 3.9, 3.10, 3.11, 3.12, CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.11.5 (main, Aug 28 2023, 16:29:45) [GCC 13.2.1 20230801]

A clear and concise description of the bug:

if an exception is active inside a coroutine/generator (coro1/agen1) and another exception is .thrown into its await coro2/yield from agen2, then coro2/agen2 loses the original exc_info.

• a generator example:

  import sys
  
  
  def outer():
      try:
          raise RuntimeError("boom")
      except RuntimeError:  # or `__exit__`/`finally`
          print(sys.exc_info())
          yield from inner()
          # note: if you inline `inner()` here, things work fine.
          print(sys.exc_info())
  
  
  def inner():
      print(sys.exc_info())
      try:
          yield
      except ValueError:
          pass
      print(sys.exc_info())
  
  
  gen = outer()
  gen.send(None)
  try:
      gen.throw(ValueError)
  except StopIteration:
      pass

  output:

  (<class 'RuntimeError'>, RuntimeError('boom'), <traceback object at 0x7fdb6b313840>)
  (<class 'RuntimeError'>, RuntimeError('boom'), <traceback object at 0x7fdb6b313840>)
  (None, None, None)
  (<class 'RuntimeError'>, RuntimeError('boom'), <traceback object at 0x7fdb6b313840>)
  

  expected output:

  same exc_info all four times.

• two coroutine examples (using asyncio in particular, with asyncio calling throw):

  import asyncio
  import sys
  from asyncio import CancelledError
  from math import inf
  
  
  async def outer():
      try:
          raise RuntimeError("boom")
      except RuntimeError:  # or `__aexit__`/`finally`
          print(sys.exc_info())
          await clean_up_and_log()
          # note: if you inline `clean_up_and_log()` here, things work fine.
          print(sys.exc_info())
  
  
  async def clean_up_and_log():
      print(sys.exc_info())
  
      # attempt to do some clean up that we are okay skipping part of if we get cancelled
      # during it or if we already have a cancellation request.
      #
      # (to reproduce, suppose that we get a cancellation request before the optional
      # clean up step.)
      asyncio.current_task().cancel()
      try:
          await asyncio.sleep(0)
      except CancelledError:
          if sys.version_info >= (3, 11):
              asyncio.current_task().uncancel()
  
      # after the optional async clean up, log the exception.
      print(sys.exc_info())
  
  
  async def clean_up_and_log():  # this example is >= 3.11 only.
      print(sys.exc_info())
  
      # attempt to do some clean up that we want to skip if it takes too long (e.g. due to
      # a non-responsive peer) or if we get cancelled during it or if we already have a
      # cancellation request.
      try:
          async with asyncio.timeout(0.1):
              await asyncio.sleep(inf)
      except TimeoutError:
          pass
      except CancelledError:
          asyncio.current_task().uncancel()
  
      # after the optional async clean up, log the exception.
      print(sys.exc_info())
  
  
  asyncio.run(outer())

  output and expected output: same as the generator example.

this problem is a special case of GH-73773 that was not discussed or fixed as part of that issue¹.

for comparison, PyPy behaves the way I expect here.