diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py index 7af8dcd526d..58607874be9 100644 --- a/Lib/collections/__init__.py +++ b/Lib/collections/__init__.py @@ -1132,10 +1132,17 @@ class UserDict(_collections_abc.MutableMapping): def __iter__(self): return iter(self.data) - # Modify __contains__ to work correctly when __missing__ is present + # Modify __contains__ and get() to work like dict + # does when __missing__ is present. def __contains__(self, key): return key in self.data + def get(self, key, default=None): + if key in self: + return self[key] + return default + + # Now, add the methods in dicts but not in MutableMapping def __repr__(self): return repr(self.data) diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py index fa1d0e014de..59b3f2ec7bf 100644 --- a/Lib/test/test_collections.py +++ b/Lib/test/test_collections.py @@ -71,6 +71,14 @@ class TestUserObjects(unittest.TestCase): obj[123] = "abc" self._copy_test(obj) + def test_dict_missing(self): + class A(UserDict): + def __missing__(self, key): + return 456 + self.assertEqual(A()[123], 456) + # get() ignores __missing__ on dict + self.assertIs(A().get(123), None) + ################################################################################ ### ChainMap (helper class for configparser and the string module) diff --git a/Misc/NEWS.d/next/Library/2020-01-09-01-57-12.bpo-39264.GsBL9-.rst b/Misc/NEWS.d/next/Library/2020-01-09-01-57-12.bpo-39264.GsBL9-.rst new file mode 100644 index 00000000000..5f9ffdffce5 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-01-09-01-57-12.bpo-39264.GsBL9-.rst @@ -0,0 +1,3 @@ +Fixed :meth:`collections.UserDict.get` to not call +:meth:`__missing__` when a value is not found. This matches the behavior of +:class:`dict`. Patch by Bar Harel.