From c3163b0297ef1ba4557f2ba6d1f207669a258c67 Mon Sep 17 00:00:00 2001 From: Chris Hunt Date: Sun, 10 Feb 2019 21:03:31 -0500 Subject: [PATCH 1/3] Failing test for dataclasses.field discarding empty mapping. --- Lib/test/test_dataclasses.py | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index ff6060c6d2838ac..ec01eb4df101961 100755 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -1737,23 +1737,25 @@ class C: i: int = field(metadata=0) # Make sure an empty dict works. + d = {} @dataclass class C: - i: int = field(metadata={}) - self.assertFalse(fields(C)[0].metadata) - self.assertEqual(len(fields(C)[0].metadata), 0) + i: int = field(metadata=d) + self.assertEqual(fields(C)[0].metadata, d) + d['foo'] = 1 + self.assertEqual(fields(C)[0].metadata, d) with self.assertRaisesRegex(TypeError, 'does not support item assignment'): fields(C)[0].metadata['test'] = 3 # Make sure a non-empty dict works. + d = {'test': 10, 'bar': '42', 3: 'three'} @dataclass class C: - i: int = field(metadata={'test': 10, 'bar': '42', 3: 'three'}) - self.assertEqual(len(fields(C)[0].metadata), 3) - self.assertEqual(fields(C)[0].metadata['test'], 10) - self.assertEqual(fields(C)[0].metadata['bar'], '42') - self.assertEqual(fields(C)[0].metadata[3], 'three') + i: int = field(metadata=d) + self.assertEqual(fields(C)[0].metadata, d) + d['foo'] = 1 + self.assertEqual(fields(C)[0].metadata, d) with self.assertRaises(KeyError): # Non-existent key. fields(C)[0].metadata['baz'] From fbc5476c4c03df45a875556518c87c46fd36c697 Mon Sep 17 00:00:00 2001 From: Chris Hunt Date: Sun, 10 Feb 2019 21:05:36 -0500 Subject: [PATCH 2/3] bpo-35960: Fix dataclasses.field throwing away empty metadata. --- Lib/dataclasses.py | 2 +- .../next/Library/2019-02-10-20-57-12.bpo-35960.bh-6Ja.rst | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2019-02-10-20-57-12.bpo-35960.bh-6Ja.rst diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 71d9896a10524a9..325b822d9f06f11 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -241,7 +241,7 @@ def __init__(self, default, default_factory, init, repr, hash, compare, self.hash = hash self.compare = compare self.metadata = (_EMPTY_METADATA - if metadata is None or len(metadata) == 0 else + if metadata is None else types.MappingProxyType(metadata)) self._field_type = None diff --git a/Misc/NEWS.d/next/Library/2019-02-10-20-57-12.bpo-35960.bh-6Ja.rst b/Misc/NEWS.d/next/Library/2019-02-10-20-57-12.bpo-35960.bh-6Ja.rst new file mode 100644 index 000000000000000..67135843877f8ce --- /dev/null +++ b/Misc/NEWS.d/next/Library/2019-02-10-20-57-12.bpo-35960.bh-6Ja.rst @@ -0,0 +1,2 @@ +Fix :func:`dataclasses.field` throwing away empty mapping objects passed as +metadata. From e302e24327110f56c4962d1fd6d4d9d02be1d9ec Mon Sep 17 00:00:00 2001 From: Chris Hunt Date: Mon, 11 Feb 2019 20:05:22 -0500 Subject: [PATCH 3/3] Add explicit tests for metadata contents. --- Lib/test/test_dataclasses.py | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index ec01eb4df101961..9c83459f09e7971 100755 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -1741,9 +1741,12 @@ class C: @dataclass class C: i: int = field(metadata=d) - self.assertEqual(fields(C)[0].metadata, d) + self.assertFalse(fields(C)[0].metadata) + self.assertEqual(len(fields(C)[0].metadata), 0) + # Update should work (see bpo-35960). d['foo'] = 1 - self.assertEqual(fields(C)[0].metadata, d) + self.assertEqual(len(fields(C)[0].metadata), 1) + self.assertEqual(fields(C)[0].metadata['foo'], 1) with self.assertRaisesRegex(TypeError, 'does not support item assignment'): fields(C)[0].metadata['test'] = 3 @@ -1753,9 +1756,14 @@ class C: @dataclass class C: i: int = field(metadata=d) - self.assertEqual(fields(C)[0].metadata, d) + self.assertEqual(len(fields(C)[0].metadata), 3) + self.assertEqual(fields(C)[0].metadata['test'], 10) + self.assertEqual(fields(C)[0].metadata['bar'], '42') + self.assertEqual(fields(C)[0].metadata[3], 'three') + # Update should work. d['foo'] = 1 - self.assertEqual(fields(C)[0].metadata, d) + self.assertEqual(len(fields(C)[0].metadata), 4) + self.assertEqual(fields(C)[0].metadata['foo'], 1) with self.assertRaises(KeyError): # Non-existent key. fields(C)[0].metadata['baz']