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$ ./python
Python 3.10.0a0 (heads/unicode_latin1:40855c7064, Jun 24 2020, 00:20:07) 
>>> import select
>>> select.epoll.register.__text_signature__
'($self, /, fd,\n eventmask=select.EPOLLIN | select.EPOLLPRI | select.EPOLLOUT)'
>>> import inspect
>>> inspect.signature(select.epoll.register)
<Signature (self, /, fd)>
=> eventmask parameter is gone!
Either signature() must raise an exception, or it must handle a __text_signature__ containing a newline character.
Issue spotted on bpo-31938 when fixing "./python -m pydoc select".
By the way, as expected, pydoc shows:
Help on method_descriptor in select.epoll:
---
$ ./python -m pydoc select.epoll.register
select.epoll.register = register(self, /, fd)
 Registers a new fd or raises an OSError if the fd is already registered.
(...)
---

Looking into this, it appears to be due to the default value and not due to the newline
I've stumbled upon two simplifications to the routines in inspect but not a fix for this
1. https://github.com/python/cpython/pull/21100
2. https://github.com/python/cpython/pull/21104
the following code is hit because `ast.literal_eval(...)` fails for the `|`d expression:
https://github.com/python/cpython/blob/2f9ada96e0d420fed0d09a032b37197f08ef167a/Lib/inspect.py#L2069-L2070
this causes the parameter to be skipped entirely