add example using leaf_generator

pep-0654.rst

@@ -393,6 +393,53 @@ recursively, as follows:
         tbs.pop()
 
 
+We can then process the full tracebacks of the leaf exceptions:
+
+.. code-block::
+
+    >>> import traceback
+    >>>
+    >>> def g(v):
+    ...     try:
+    ...         raise ValueError(v)
+    ...     except Exception as e:
+    ...         return e
+    ...
+    >>> def f():
+    ...     raise ExceptionGroup("eg", [g(1), g(2)])
+    ...
+    >>> try:
+    ...     f()
+    ... except BaseException as e:
+    ...     eg = e
+    ...
+    >>> for (i, (exc, tbs)) in enumerate(leaf_generator(eg)):
+    ...     print(f"\n>>> Exception #{i+1}:")
+    ...     traceback.print_exception(exc)
+    ...     print(f"The complete traceback for Exception #{i+1}:")
+    ...     for tb in tbs:
+    ...         traceback.print_tb(tb)
+    ...
+
+    >>> Exception #1:
+    Traceback (most recent call last):
+      File "<stdin>", line 3, in g
+    ValueError: 1
+    The complete traceback for Exception #1
+    File "<stdin>", line 2, in <module>
+      File "<stdin>", line 2, in f
+      File "<stdin>", line 3, in g
+
+    >>> Exception #2:
+    Traceback (most recent call last):
+      File "<stdin>", line 3, in g
+    ValueError: 2
+    The complete traceback for Exception #2:
+      File "<stdin>", line 2, in <module>
+      File "<stdin>", line 2, in f
+      File "<stdin>", line 3, in g
+    >>>
+
 except*
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