gh-120521: clarify except* documentation to allow tuples (#120523)

Co-authored-by: Jelle Zijlstra <[email protected]>
Co-authored-by: Irit Katriel <[email protected]>

Author: 3 people

Doc/reference/compound_stmts.rst

@@ -245,13 +245,12 @@ handler is started. This search inspects the :keyword:`!except` clauses in turn
 until one is found that matches the exception.
 An expression-less :keyword:`!except` clause, if present, must be last;
 it matches any exception.
-For an :keyword:`!except` clause with an expression,
-that expression is evaluated, and the clause matches the exception
-if the resulting object is "compatible" with the exception.  An object is
-compatible with an exception if the object is the class or a
-:term:`non-virtual base class <abstract base class>` of the exception object,
-or a tuple containing an item that is the class or a non-virtual base class
-of the exception object.
+
+For an :keyword:`!except` clause with an expression, the
+expression must evaluate to an exception type or a tuple of exception types.
+The raised exception matches an :keyword:`!except` clause whose expression evaluates
+to the class or a :term:`non-virtual base class <abstract base class>` of the exception object,
+or to a tuple that contains such a class.
 
 If no :keyword:`!except` clause matches the exception,
 the search for an exception handler
@@ -378,8 +377,10 @@ exception group with an empty message string. ::
    ...
    ExceptionGroup('', (BlockingIOError()))
 
-An :keyword:`!except*` clause must have a matching type,
-and this type cannot be a subclass of :exc:`BaseExceptionGroup`.
+An :keyword:`!except*` clause must have a matching expression; it cannot be ``except*:``.
+Furthermore, this expression cannot contain exception group types, because that would
+have ambiguous semantics.
+
 It is not possible to mix :keyword:`except` and :keyword:`!except*`
 in the same :keyword:`try`.
 :keyword:`break`, :keyword:`continue` and :keyword:`return`