Don't show context in from None

Author: Carreau

Lib/pdb.py

@@ -421,11 +421,18 @@ def interaction(self, frame, tb_or_exc):
 
         if isinstance(tb_or_exc, BaseException):
             tb_or_exc, exception = tb_or_exc.__traceback__, tb_or_exc
-            self._chained_exceptions = [exception]
+            self._chained_exceptions = []
+            self._chained_exception_index = -1
             current = exception
-            while current := (current.__cause__ or current.__context__):
+            while current:
                 self._chained_exception_index += 1
                 self._chained_exceptions.insert(0, current)
+                if current.__cause__:
+                    current = current.__cause__
+                elif current.__context__ and not current.__suppress_context__:
+                    current = current.__context__
+                else:
+                    current = None
         else:
             self._chained_exceptions = []
 

Lib/test/test_pdb.py

@@ -1027,6 +1027,45 @@ def test_post_mortem_context_of_the_cause():
     """
 
 
+def test_post_mortem_from_none():
+    """Test post mortem traceback debugging of chained exception
+
+    In particular that cause from None (which sets __supress_context__ to True)
+    does not show context.
+
+
+    >>> def main():
+    ...     try:
+    ...         raise TypeError('Context of the cause')
+    ...     except Exception as e1:
+    ...         raise ValueError("With Cause, and cause has context") from None
+
+    >>> def test_function():
+    ...     import pdb;
+    ...     instance = pdb.Pdb(nosigint=True, readrc=False)
+    ...     try:
+    ...         main()
+    ...     except Exception as e:
+    ...         # same as pdb.post_mortem(e), but with custom pdb instance.
+    ...         instance.reset()
+    ...         instance.interaction(None, e)
+
+    >>> with PdbTestInput([  # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE
+    ...     'exceptions',
+    ...     'exit',
+    ... ]):
+    ...    try:
+    ...        test_function()
+    ...    except ValueError:
+    ...        print('Correctly reraised.')
+    > <doctest test.test_pdb.test_post_mortem_from_none[0]>(5)main()
+    -> raise ValueError("With Cause, and cause has context") from None
+    (Pdb) exceptions
+    > 0 ValueError('With Cause, and cause has context')
+    (Pdb) exit
+    """
+
+
 def test_post_mortem():
     """Test post mortem traceback debugging.