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gh-94808: add tests covering PySequence_[InPlace]Concat #99319

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gh-94808: add tests covering `PySequence_[InPlace]Concat`
sobolevn Nov 10, 2022
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Merge branch 'main' into cover-sequence-concat
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40 changes: 26 additions & 14 deletions Lib/test/test_operator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -531,27 +531,33 @@ def test_concat(self):
self.assertEqual(data2, 'ab') # must not change

# Subclasses:
class ListSubclass(list): ...
class ListSubclass(list):
pass

data1 = ListSubclass([1, 2])
data2 = ListSubclass(['a', 'b'])
self.assertEqual(operator.concat(data1, data2),
ListSubclass([1, 2, 'a', 'b']))
self.assertEqual(operator.concat(data1, data2), data1 + data2)

res = operator.concat(data1, data2)
self.assertIsInstance(res, list)
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This doesn't prove anything, does it? Whether the result is a ListSubclass or a plain list, this will always be true. If you want to say something interesting here I'd assert that it isn't a ListSubclass instance.

self.assertEqual(res, [1, 2, 'a', 'b'])
self.assertIsInstance(data1, ListSubclass)
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I don't see the point of this -- of course data1 and data2 are instances of ListSubclass, that's how they were created.

self.assertEqual(data1, ListSubclass([1, 2])) # must not change
self.assertIsInstance(data2, ListSubclass)
self.assertEqual(data2, ListSubclass(['a', 'b'])) # must not change

# Custom type with `__add__`:
class TupleSubclass(tuple):
def __add__(self, other):
return other + self
return TupleSubclass(other + self)

data1 = TupleSubclass([1, 2])
data2 = ('a', 'b')
self.assertEqual(operator.concat(data1, data2),
TupleSubclass(['a', 'b', 1, 2]))
self.assertEqual(operator.concat(data1, data2), data1 + data2)
res = operator.concat(data1, data2)
self.assertIsInstance(res, TupleSubclass)
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This one is good.

self.assertEqual(res, TupleSubclass(['a', 'b', 1, 2]))
self.assertIsInstance(data1, TupleSubclass)
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But this is still questionable. I can't think of a scenario where this would fail.

Or do you have coverage results showing this is needed? (Where?)

Ditto for data2 and again in the following block of tests.

self.assertEqual(data1, TupleSubclass([1, 2])) # must not change
self.assertIsInstance(data2, tuple)
self.assertEqual(data2, ('a', 'b')) # must not change

# Corner cases:
Expand Down Expand Up @@ -599,26 +605,32 @@ def test_iconcat(self):
self.assertEqual(data2, 'ab') # must not change

# Subclasses:
class ListSubclass(list): ...
class ListSubclass(list):
pass

data1 = ListSubclass([1, 2])
data2 = ListSubclass(['a', 'b'])
res = operator.iconcat(data1, data2)
self.assertEqual(res, ListSubclass([1, 2, 'a', 'b']))
self.assertIsInstance(res, ListSubclass)
self.assertEqual(res, [1, 2, 'a', 'b'])
self.assertIsInstance(data1, ListSubclass)
self.assertEqual(data1, ListSubclass([1, 2, 'a', 'b'])) # must change
self.assertIsInstance(data2, ListSubclass)
self.assertEqual(data2, ListSubclass(['a', 'b'])) # must not change

# Custom type with `__add__`:
class TupleSubclass(tuple):
def __add__(self, other):
return other + self
return TupleSubclass(other + self)

data1 = TupleSubclass([1, 2])
data2 = ('a', 'b')
self.assertEqual(operator.iconcat(data1, data2),
TupleSubclass(['a', 'b', 1, 2]))
self.assertEqual(operator.iconcat(data1, data2), data1 + data2)
res = operator.iconcat(data1, data2)
self.assertIsInstance(res, TupleSubclass)
self.assertEqual(res, TupleSubclass(['a', 'b', 1, 2]))
self.assertIsInstance(data1, TupleSubclass)
self.assertEqual(data1, TupleSubclass([1, 2])) # must not change
self.assertIsInstance(data2, tuple)
self.assertEqual(data2, ('a', 'b')) # must not change

# Corner cases:
Expand Down