Silently ignore unregistering closed files. Fixes issue 19876. With docs and slight test refactor.
diff --git a/Doc/library/selectors.rst b/Doc/library/selectors.rst
index b0b002f..98377c8 100644
--- a/Doc/library/selectors.rst
+++ b/Doc/library/selectors.rst
@@ -102,7 +102,8 @@
Register a file object for selection, monitoring it for I/O events.
- *fileobj* is the file object to monitor.
+ *fileobj* is the file object to monitor. It may either be an integer
+ file descriptor or an object with a ``fileno()`` method.
*events* is a bitwise mask of events to monitor.
*data* is an opaque object.
@@ -118,7 +119,9 @@
*fileobj* must be a file object previously registered.
This returns the associated :class:`SelectorKey` instance, or raises a
- :exc:`KeyError` if the file object is not registered.
+ :exc:`KeyError` if *fileobj* is not registered. It will raise
+ :exc:`ValueError` if *fileobj* is invalid (e.g. it has no ``fileno()``
+ method or its ``fileno()`` method has an invalid return value).
.. method:: modify(fileobj, events, data=None)