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bpo-34427: islice values when calling MutableSequence.extend on self #8813

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Merged
rhettinger merged 6 commits into from
Aug 30, 2018
Merged

bpo-34427: islice values when calling MutableSequence.extend on self #8813

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4766377
islice values when calling MutableSequence.extend on self
KittenHero Aug 19, 2018
351ea2b
create copy using list(values)
KittenHero Aug 20, 2018
7183136
added tests to mutable sequence subclass
KittenHero Aug 20, 2018
7dea2ab
news for behaviour change
KittenHero Aug 20, 2018
89f6ab2
fixed test
KittenHero Aug 20, 2018
594ed4a
Make the blurb entry more specific.
rhettinger Aug 27, 2018
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2 changes: 2 additions & 0 deletions Lib/_collections_abc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -986,6 +986,8 @@ def reverse(self):

def extend(self, values):
'S.extend(iterable) -- extend sequence by appending elements from the iterable'
if values is self:
values = list(values)
for v in values:
self.append(v)

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12 changes: 12 additions & 0 deletions Lib/test/test_collections.py
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Expand Up @@ -1721,6 +1721,18 @@ def insert(self, index, value):
mss.clear()
self.assertEqual(len(mss), 0)

# issue 34427
# extending self should not cause infinite loop
items = 'ABCD'
mss2 = MutableSequenceSubclass()
mss2.extend(items + items)
mss.clear()
mss.extend(items)
mss.extend(mss)
self.assertEqual(len(mss), len(mss2))
self.assertEqual(list(mss), list(mss2))


################################################################################
### Counter
################################################################################
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-08-20-13-53-10.bpo-34427.tMRQjl.rst
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@@ -0,0 +1 @@
Fix infinite loop in ``a.extend(a)`` for ``MutableSequence`` subclasses.