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gh-158234: Fix typo in tracemalloc cumulative mode error message #158233

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gh-158234: Fix typo in tracemalloc cumulative mode error message #158233

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17 changes: 17 additions & 0 deletions Lib/test/test_tracemalloc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -598,6 +598,23 @@ def test_snapshot_group_by_traceback(self):
self.assertRaises(ValueError,
snapshot.statistics, 'traceback', cumulative=True)

def test_compare_to_does_not_mutate_group(self):
# gh-158232: _compare_grouped_stats() used to pop from old_group,
# silently draining the caller's dict.
tb_a = traceback(('f.py', 1))
tb_b = traceback(('f.py', 2))
tb_c = traceback(('f.py', 3))

old = {tb_a: tracemalloc.Statistic(tb_a, 100, 2),
tb_b: tracemalloc.Statistic(tb_b, 50, 1)}
new = {tb_a: tracemalloc.Statistic(tb_a, 200, 3),
tb_c: tracemalloc.Statistic(tb_c, 10, 1)}
old_copy = dict(old)

tracemalloc._compare_grouped_stats(old, new)

self.assertEqual(old, old_copy)

Comment on lines +601 to +617

@StanFromIreland StanFromIreland Sep 27, 2026

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Suggested change
def test_compare_to_does_not_mutate_group(self):
# gh-158232: _compare_grouped_stats() used to pop from old_group,
# silently draining the caller's dict.
tb_a = traceback(('f.py', 1))
tb_b = traceback(('f.py', 2))
tb_c = traceback(('f.py', 3))
old = {tb_a: tracemalloc.Statistic(tb_a, 100, 2),
tb_b: tracemalloc.Statistic(tb_b, 50, 1)}
new = {tb_a: tracemalloc.Statistic(tb_a, 200, 3),
tb_c: tracemalloc.Statistic(tb_c, 10, 1)}
old_copy = dict(old)
tracemalloc._compare_grouped_stats(old, new)
self.assertEqual(old, old_copy)

I'd prefer we drop the test. The name is wrong, it's placed oddly, and it refers to a different issue. It also tests an implementation detail.

def test_snapshot_group_by_cumulative(self):
snapshot, snapshot2 = create_snapshots()
tb_0 = traceback_filename('<unknown>')
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3 changes: 2 additions & 1 deletion Lib/tracemalloc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,7 @@ def _sort_key(self):

def _compare_grouped_stats(old_group, new_group):
statistics = []
old_group = dict(old_group)
for traceback, stat in new_group.items():
previous = old_group.pop(traceback, None)
if previous is not None:
Expand Down Expand Up @@ -478,7 +479,7 @@ def _group_by(self, key_type, cumulative):
if key_type not in ('traceback', 'filename', 'lineno'):
raise ValueError("unknown key_type: %r" % (key_type,))
if cumulative and key_type not in ('lineno', 'filename'):
raise ValueError("cumulative mode cannot by used "
raise ValueError("cumulative mode cannot be used "
"with key type %r" % key_type)

stats = {}
Expand Down
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