[Python-checkins] bpo-31299: make it possible to filter out frames from tracebacks (GH-28067)

[iritkatriel]

https://github.com/python/cpython/commit/863154c9292e70c5a8a1a3f22ef4ee42e2304281
commit: 863154c9292e70c5a8a1a3f22ef4ee42e2304281
branch: main
author: Irit Katriel <1055913+iritkatriel at users.noreply.github.com>
committer: iritkatriel <1055913+iritkatriel at users.noreply.github.com>
date: 2021-08-31T21:42:08+01:00
summary:

bpo-31299: make it possible to filter out frames from tracebacks (GH-28067)

files:
A Misc/NEWS.d/next/Library/2021-08-30-13-55-09.bpo-31299.9QzjZs.rst
M Doc/library/traceback.rst
M Lib/test/test_traceback.py
M Lib/traceback.py

diff --git a/Doc/library/traceback.rst b/Doc/library/traceback.rst
index 83d5c8c6fcbd3..7b230495b7b56 100644
--- a/Doc/library/traceback.rst
+++ b/Doc/library/traceback.rst
@@ -357,7 +357,8 @@ capture data for later printing in a lightweight fashion.
 
       Returns a string for printing one of the frames involved in the stack.
       This method gets called for each frame object to be printed in the
-      :class:`StackSummary`.
+      :class:`StackSummary`. If it returns ``None``, the frame is omitted
+      from the output.
 
       .. versionadded:: 3.11
 
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 5d48e9d7ff039..d1967aabb29a1 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -1514,6 +1514,34 @@ def some_inner():
             s.format(),
             [f'{__file__}:{some_inner.__code__.co_firstlineno + 1}'])
 
+    def test_dropping_frames(self):
+         def f():
+             1/0
+
+         def g():
+             try:
+                 f()
+             except:
+                 return sys.exc_info()
+
+         exc_info = g()
+
+         class Skip_G(traceback.StackSummary):
+             def format_frame(self, frame):
+                 if frame.name == 'g':
+                     return None
+                 return super().format_frame(frame)
+
+         stack = Skip_G.extract(
+             traceback.walk_tb(exc_info[2])).format()
+
+         self.assertEqual(len(stack), 1)
+         lno = f.__code__.co_firstlineno + 1
+         self.assertEqual(
+             stack[0],
+             f'  File "{__file__}", line {lno}, in f\n    1/0\n'
+         )
+
 
 class TestTracebackException(unittest.TestCase):
 
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 4ad8c9a17b349..8d83fd9b517e6 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -515,6 +515,9 @@ def format(self):
         last_name = None
         count = 0
         for frame in self:
+            formatted_frame = self.format_frame(frame)
+            if formatted_frame is None:
+                continue
             if (last_file is None or last_file != frame.filename or
                 last_line is None or last_line != frame.lineno or
                 last_name is None or last_name != frame.name):
diff --git a/Misc/NEWS.d/next/Library/2021-08-30-13-55-09.bpo-31299.9QzjZs.rst b/Misc/NEWS.d/next/Library/2021-08-30-13-55-09.bpo-31299.9QzjZs.rst
new file mode 100644
index 0000000000000..1ffa0b15172ee
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-08-30-13-55-09.bpo-31299.9QzjZs.rst
@@ -0,0 +1 @@
+Add option to completely drop frames from a traceback by returning ``None`` from a :meth:`~traceback.StackSummary.format_frame` override.
\ No newline at end of file