#1565525: Add traceback.clear_frames() helper function to clear locals ref'd by a traceback

2 files changed, 42 insertions, 1 deletions

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 66a12bf..96ef951 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -388,6 +388,36 @@ class CExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
         return s.getvalue()
 
 
+class MiscTracebackCases(unittest.TestCase):
+    #
+    # Check non-printing functions in traceback module
+    #
+
+    def test_clear(self):
+        def outer():
+            middle()
+        def middle():
+            inner()
+        def inner():
+            i = 1
+            1/0
+
+        try:
+            outer()
+        except:
+            type_, value, tb = sys.exc_info()
+
+        # Initial assertion: there's one local in the inner frame.
+        inner_frame = tb.tb_next.tb_next.tb_next.tb_frame
+        self.assertEqual(len(inner_frame.f_locals), 1)
+
+        # Clear traceback frames
+        traceback.clear_frames(tb)
+
+        # Local variable dict should now be empty.
+        self.assertEqual(len(inner_frame.f_locals), 0)
+
+
 def test_main():
     run_unittest(__name__)
 
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 3aa1578..d5b3752 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -7,7 +7,8 @@ import operator
 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
            'format_tb', 'print_exc', 'format_exc', 'print_exception',
-           'print_last', 'print_stack', 'print_tb']
+           'print_last', 'print_stack', 'print_tb',
+           'clear_frames']
 
 #
 # Formatting and printing lists of traceback lines.
@@ -299,3 +300,13 @@ def extract_stack(f=None, limit=None):
     stack = list(_extract_stack_iter(_get_stack(f), limit=limit))
     stack.reverse()
     return stack
+
+def clear_frames(tb):
+    "Clear all references to local variables in the frames of a traceback."
+    while tb is not None:
+        try:
+            tb.tb_frame.clear()
+        except RuntimeError:
+            # Ignore the exception raised if the frame is still executing.
+            pass
+        tb = tb.tb_next