bpo-43764: Add match_args=False parameter to dataclass decorator and to make_dataclasses function. (GH-25337)
Add match_args=False parameter to dataclass decorator and to make_dataclass function.
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index ceda822..e8eb206 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -154,12 +154,17 @@
# __match_args__
#
-# | no | yes | <--- class has __match_args__ in __dict__?
-# +=======+=======+
-# | add | | <- the default
-# +=======+=======+
-# __match_args__ is always added unless the class already defines it. It is a
-# tuple of __init__ parameter names; non-init fields must be matched by keyword.
+# +--- match_args= parameter
+# |
+# v | | |
+# | no | yes | <--- class has __match_args__ in __dict__?
+# +=======+=======+=======+
+# | False | | |
+# +-------+-------+-------+
+# | True | add | | <- the default
+# +=======+=======+=======+
+# __match_args__ is a tuple of __init__ parameter names; non-init fields must
+# be matched by keyword.
# Raised when an attempt is made to modify a frozen class.
@@ -830,7 +835,8 @@ def _hash_exception(cls, fields, globals):
# version of this table.
-def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
+def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,
+ match_args):
# 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
@@ -1016,8 +1022,9 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
cls.__doc__ = (cls.__name__ +
str(inspect.signature(cls)).replace(' -> NoneType', ''))
- if '__match_args__' not in cls.__dict__:
- cls.__match_args__ = tuple(f.name for f in field_list if f.init)
+ if match_args:
+ _set_new_attribute(cls, '__match_args__',
+ tuple(f.name for f in field_list if f.init))
abc.update_abstractmethods(cls)
@@ -1025,7 +1032,7 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
def dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False,
- unsafe_hash=False, frozen=False):
+ unsafe_hash=False, frozen=False, match_args=True):
"""Returns the same class as was passed in, with dunder methods
added based on the fields defined in the class.
@@ -1035,11 +1042,13 @@ def dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False,
repr is true, a __repr__() method is added. If order is true, rich
comparison dunder methods are added. If unsafe_hash is true, a
__hash__() method function is added. If frozen is true, fields may
- not be assigned to after instance creation.
+ not be assigned to after instance creation. If match_args is true,
+ the __match_args__ tuple is added.
"""
def wrap(cls):
- return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
+ return _process_class(cls, init, repr, eq, order, unsafe_hash,
+ frozen, match_args)
# See if we're being called as @dataclass or @dataclass().
if cls is None:
@@ -1198,7 +1207,7 @@ 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):
+ frozen=False, match_args=True):
"""Return a new dynamically created dataclass.
The dataclass name will be 'cls_name'. 'fields' is an iterable
@@ -1259,7 +1268,8 @@ class C(Base):
# of generic dataclassses.
cls = types.new_class(cls_name, bases, {}, lambda ns: ns.update(namespace))
return dataclass(cls, init=init, repr=repr, eq=eq, order=order,
- unsafe_hash=unsafe_hash, frozen=frozen)
+ unsafe_hash=unsafe_hash, frozen=frozen,
+ match_args=match_args)
def replace(obj, /, **changes):
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 29f29e1..4beed69 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3440,6 +3440,47 @@ class X:
c: int
self.assertEqual(X.__match_args__, ("a", "b", "c"))
+ def test_match_args_argument(self):
+ @dataclass(match_args=False)
+ class X:
+ a: int
+ self.assertNotIn('__match_args__', X.__dict__)
+
+ @dataclass(match_args=False)
+ class Y:
+ a: int
+ __match_args__ = ('b',)
+ self.assertEqual(Y.__match_args__, ('b',))
+
+ @dataclass(match_args=False)
+ class Z(Y):
+ z: int
+ self.assertEqual(Z.__match_args__, ('b',))
+
+ # Ensure parent dataclass __match_args__ is seen, if child class
+ # specifies match_args=False.
+ @dataclass
+ class A:
+ a: int
+ z: int
+ @dataclass(match_args=False)
+ class B(A):
+ b: int
+ self.assertEqual(B.__match_args__, ('a', 'z'))
+
+ def test_make_dataclasses(self):
+ C = make_dataclass('C', [('x', int), ('y', int)])
+ self.assertEqual(C.__match_args__, ('x', 'y'))
+
+ C = make_dataclass('C', [('x', int), ('y', int)], match_args=True)
+ self.assertEqual(C.__match_args__, ('x', 'y'))
+
+ C = make_dataclass('C', [('x', int), ('y', int)], match_args=False)
+ self.assertNotIn('__match__args__', C.__dict__)
+
+ C = make_dataclass('C', [('x', int), ('y', int)], namespace={'__match_args__': ('z',)})
+ self.assertEqual(C.__match_args__, ('z',))
+
if __name__ == '__main__':
unittest.main()