bpo-42269: Add slots parameter to dataclass decorator (GH-24171)
Add slots parameter to dataclass decorator and make_dataclass function.
diff --git a/Doc/library/dataclasses.rst b/Doc/library/dataclasses.rst
index 0e8db50..dbbc5d6 100644
--- a/Doc/library/dataclasses.rst
+++ b/Doc/library/dataclasses.rst
@@ -46,7 +46,7 @@
Module-level decorators, classes, and functions
-----------------------------------------------
-.. decorator:: dataclass(*, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False)
+.. decorator:: dataclass(*, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False)
This function is a :term:`decorator` that is used to add generated
:term:`special method`\s to classes, as described below.
@@ -79,7 +79,7 @@
class C:
...
- @dataclass(init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False)
+ @dataclass(init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False)
class C:
...
@@ -173,6 +173,11 @@
glossary entry for details. Also see the ``dataclasses.KW_ONLY``
section.
+ - ``slots``: If true (the default is ``False``), :attr:`__slots__` attribute
+ will be generated and new class will be returned instead of the original one.
+ If :attr:`__slots__` is already defined in the class, then :exc:`TypeError`
+ is raised.
+
``field``\s may optionally specify a default value, using normal
Python syntax::
@@ -337,7 +342,7 @@
Raises :exc:`TypeError` if ``instance`` is not a dataclass instance.
-.. function:: make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False)
+.. function:: make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False)
Creates a new dataclass with name ``cls_name``, fields as defined
in ``fields``, base classes as given in ``bases``, and initialized
@@ -346,8 +351,8 @@
or ``(name, type, Field)``. If just ``name`` is supplied,
``typing.Any`` is used for ``type``. The values of ``init``,
``repr``, ``eq``, ``order``, ``unsafe_hash``, ``frozen``,
- ``match_args``, and ``kw_only`` have the same meaning as they do
- in :func:`dataclass`.
+ ``match_args``, ``kw_only``, and ``slots`` have the same meaning as
+ they do in :func:`dataclass`.
This function is not strictly required, because any Python
mechanism for creating a new class with ``__annotations__`` can
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index 1a39066..9c8e296 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -895,6 +895,12 @@
they are provided by the underlying curses library.
(Contributed by Zackery Spytz in :issue:`39273`.)
+dataclasses
+-----------
+
+Added ``slots`` parameter in :func:`dataclasses.dataclass` decorator.
+(Contributed by Yurii Karabas in :issue:`42269`)
+
.. _distutils-deprecated:
distutils
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 3de50cf..5e57163 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -874,7 +874,7 @@ def _hash_exception(cls, fields, globals):
def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,
- match_args, kw_only):
+ match_args, kw_only, slots):
# Now that dicts retain insertion order, there's no reason to use
# an ordered dict. I am leveraging that ordering here, because
# derived class fields overwrite base class fields, but the order
@@ -1086,14 +1086,46 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,
_set_new_attribute(cls, '__match_args__',
tuple(f.name for f in std_init_fields))
+ if slots:
+ cls = _add_slots(cls)
+
abc.update_abstractmethods(cls)
return cls
+def _add_slots(cls):
+ # Need to create a new class, since we can't set __slots__
+ # after a class has been created.
+
+ # Make sure __slots__ isn't already set.
+ if '__slots__' in cls.__dict__:
+ raise TypeError(f'{cls.__name__} already specifies __slots__')
+
+ # Create a new dict for our new class.
+ cls_dict = dict(cls.__dict__)
+ field_names = tuple(f.name for f in fields(cls))
+ cls_dict['__slots__'] = field_names
+ for field_name in field_names:
+ # Remove our attributes, if present. They'll still be
+ # available in _MARKER.
+ cls_dict.pop(field_name, None)
+
+ # Remove __dict__ itself.
+ cls_dict.pop('__dict__', None)
+
+ # And finally create the class.
+ qualname = getattr(cls, '__qualname__', None)
+ cls = type(cls)(cls.__name__, cls.__bases__, cls_dict)
+ if qualname is not None:
+ cls.__qualname__ = qualname
+
+ return cls
+
+
def dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False,
unsafe_hash=False, frozen=False, match_args=True,
- kw_only=False):
+ kw_only=False, slots=False):
"""Returns the same class as was passed in, with dunder methods
added based on the fields defined in the class.
@@ -1105,12 +1137,13 @@ def dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False,
__hash__() method function is added. If frozen is true, fields may
not be assigned to after instance creation. If match_args is true,
the __match_args__ tuple is added. If kw_only is true, then by
- default all fields are keyword-only.
+ default all fields are keyword-only. If slots is true, an
+ __slots__ attribute is added.
"""
def wrap(cls):
return _process_class(cls, init, repr, eq, order, unsafe_hash,
- frozen, match_args, kw_only)
+ frozen, match_args, kw_only, slots)
# See if we're being called as @dataclass or @dataclass().
if cls is None:
@@ -1269,7 +1302,7 @@ def _astuple_inner(obj, tuple_factory):
def make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True,
repr=True, eq=True, order=False, unsafe_hash=False,
- frozen=False, match_args=True):
+ frozen=False, match_args=True, slots=False):
"""Return a new dynamically created dataclass.
The dataclass name will be 'cls_name'. 'fields' is an iterable
@@ -1336,7 +1369,7 @@ def exec_body_callback(ns):
# Apply the normal decorator.
return dataclass(cls, init=init, repr=repr, eq=eq, order=order,
unsafe_hash=unsafe_hash, frozen=frozen,
- match_args=match_args)
+ match_args=match_args, slots=slots)
def replace(obj, /, **changes):
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 670648a..2fa0ae0 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -2781,6 +2781,59 @@ class Derived(Base):
# We can add a new field to the derived instance.
d.z = 10
+ def test_generated_slots(self):
+ @dataclass(slots=True)
+ class C:
+ x: int
+ y: int
+
+ c = C(1, 2)
+ self.assertEqual((c.x, c.y), (1, 2))
+
+ c.x = 3
+ c.y = 4
+ self.assertEqual((c.x, c.y), (3, 4))
+
+ with self.assertRaisesRegex(AttributeError, "'C' object has no attribute 'z'"):
+ c.z = 5
+
+ def test_add_slots_when_slots_exists(self):
+ with self.assertRaisesRegex(TypeError, '^C already specifies __slots__$'):
+ @dataclass(slots=True)
+ class C:
+ __slots__ = ('x',)
+ x: int
+
+ def test_generated_slots_value(self):
+ @dataclass(slots=True)
+ class Base:
+ x: int
+
+ self.assertEqual(Base.__slots__, ('x',))
+
+ @dataclass(slots=True)
+ class Delivered(Base):
+ y: int
+
+ self.assertEqual(Delivered.__slots__, ('x', 'y'))
+
+ @dataclass
+ class AnotherDelivered(Base):
+ z: int
+
+ self.assertTrue('__slots__' not in AnotherDelivered.__dict__)
+
+ def test_returns_new_class(self):
+ class A:
+ x: int
+
+ B = dataclass(A, slots=True)
+ self.assertIsNot(A, B)
+
+ self.assertFalse(hasattr(A, "__slots__"))
+ self.assertTrue(hasattr(B, "__slots__"))
+
+
class TestDescriptors(unittest.TestCase):
def test_set_name(self):
# See bpo-33141.
diff --git a/Misc/NEWS.d/next/Library/2021-01-08-22-32-13.bpo-42269.W5v8z4.rst b/Misc/NEWS.d/next/Library/2021-01-08-22-32-13.bpo-42269.W5v8z4.rst
new file mode 100644
index 0000000..595f873
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-01-08-22-32-13.bpo-42269.W5v8z4.rst
@@ -0,0 +1,3 @@
+Add ``slots`` parameter to ``dataclasses.dataclass`` decorator to
+automatically generate ``__slots__`` for class. Patch provided by Yurii
+Karabas.