Merge pull request #187 from zopefoundation/tb_format_signatures

make signatures in `tb_format` compatible with Python 3.12+

CHANGES.rst

@@ -5,7 +5,8 @@
 6.7 (unreleased)
 ================
 
-- Nothing changed yet.
+- Make signatures in ``tb_format`` Python 3.12+ compatible
+  (`#186 <https://github.com/zopefoundation/zope.testrunner/issues/186>`_)
 
 
 6.6 (2024-10-16)

src/zope/testrunner/tb_format.py

@@ -22,6 +22,20 @@
 import zope.testrunner.feature
 
 
+try:
+    from traceback import _parse_value_tb
+    from traceback import _sentinel
+except ImportError:
+    # before 3.10
+    # for Python before 3.10, the first 3 parameters of
+    # ``print_exception`` and ``format_exception`` are all mandatory
+    # and the first one (``etype`` alias ``t``) is ignored
+    _sentinel = object()
+
+    def _parse_value_tb(ignored, value, tb):
+        return value, tb
+
+
 def _iter_chain(exc, custom_tb=None, seen=None):
     if seen is None:
         seen = set()
@@ -43,21 +57,8 @@ def _iter_chain(exc, custom_tb=None, seen=None):
         yield from it
 
 
-def _parse_value_tb(exc, value, tb):
-    # Taken straight from the traceback module code on Python 3.10, which
-    # introduced the ability to call print_exception with an exception
-    # instance as first parameter
-    if (value is None) != (tb is None):
-        raise ValueError("Both or neither of value and tb must be given")
-    if value is tb is None:
-        if exc is not None:
-            return exc, exc.__traceback__
-        else:
-            return None, None
-    return value, tb
-
-
-def format_exception(t, v, tb, limit=None, chain=None):
+def format_exception(t, value=_sentinel, tb=_sentinel, limit=None, chain=None):
+    v, tb = _parse_value_tb(t, value, tb)
     if chain:
         values = _iter_chain(v, tb)
     else:
@@ -70,8 +71,9 @@ def format_exception(t, v, tb, limit=None, chain=None):
         return fmt.formatException(t, v, tb)
 
 
-def print_exception(t, v=None, tb=None, limit=None, file=None, chain=None):
-    v, tb = _parse_value_tb(t, v, tb)
+def print_exception(t, value=_sentinel, tb=_sentinel,
+                    limit=None, file=None, chain=None):
+    v, tb = _parse_value_tb(t, value, tb)
     if chain:
         values = _iter_chain(v, tb)
     else: