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bpo-27639: Correct return type for UserList slicing operation (#13169) 

* BPO-27639: Correct return type for UserList slicing operation

Added logic to __getitem__ magic method for UserList to ensure that the return
type matches that of self.
This commit is contained in:
Michael Blahay 2019-05-07 17:41:06 -04:00 committed by Mark Shannon
parent ca87eebb22
commit b1c3167c23
3 changed files with 13 additions and 1 deletions
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6
Lib/collections/__init__.py
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@ -1085,7 +1085,11 @@ class UserList(_collections_abc.MutableSequence):
return other.data if isinstance(other, UserList) else other return other.data if isinstance(other, UserList) else other
def __contains__(self, item): return item in self.data def __contains__(self, item): return item in self.data
def __len__(self): return len(self.data) def __len__(self): return len(self.data)
def __getitem__(self, i): return self.data[i] def __getitem__(self, i):
if isinstance(i, slice):
return self.__class__(self.data[i])
else:
return self.data[i]
def __setitem__(self, i, item): self.data[i] = item def __setitem__(self, i, item): self.data[i] = item
def __delitem__(self, i): del self.data[i] def __delitem__(self, i): del self.data[i]
def __add__(self, other): def __add__(self, other):

6
Lib/test/test_userlist.py
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@ -17,6 +17,12 @@ class UserListTest(list_tests.CommonTest):
for j in range(-3, 6): for j in range(-3, 6):
self.assertEqual(u[i:j], l[i:j]) self.assertEqual(u[i:j], l[i:j])
def test_slice_type(self):
l = [0, 1, 2, 3, 4]
u = UserList(l)
self.assertIsInstance(u[:], u.__class__)
self.assertEqual(u[:],u)
def test_add_specials(self): def test_add_specials(self):
u = UserList("spam") u = UserList("spam")
u2 = u + "eggs" u2 = u + "eggs"

2
Misc/NEWS.d/next/Core and Builtins/2019-05-07-15-49-17.bpo-27639.b1Ah87.rst Normal file
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@ -0,0 +1,2 @@
Correct return type for UserList slicing operations. Patch by Michael Blahay,
Erick Cervantes, and vaultah