Add 'factory' support for the Any trait type

docs/source/traits_user_manual/defining.rst

@@ -278,7 +278,9 @@ the table.
 +------------------+----------------------------------------------------------+
 | Name             | Callable Signature                                       |
 +==================+==========================================================+
-| Any              | Any( [*value* = None, \*\*\ *metadata*] )                |
+| Any              | Any( [*default_value* = None, \*,                        |
+|                  | *factory* = None, *args* = (), *kw* = {},                |
+|                  | \*\*\ *metadata* )                                       |
 +------------------+----------------------------------------------------------+
 | Array            | Array( [*dtype* = None, *shape* = None, *value* = None,  |
 |                  | *typecode* = None, \*\*\ *metadata*] )                   |

traits-stubs/traits-stubs/trait_types.pyi

@@ -42,7 +42,18 @@ _S = TypeVar("_S")
 
 _Trait = _Union[_TraitType[_S, _T], _Type[_TraitType[_S, _T]]]
 
-Any = _Any
+
+class Any(_TraitType[_Any, _Any]):
+    def __init__(
+        self,
+        default_value: _Any = ...,
+        *,
+        factory: _CallableType = ...,
+        args: tuple = ...,
+        kw: dict = ...,
+        **metadata: _Any,
+    ) -> None:
+        ...
 
 
 class _BaseInt(_TraitType[_T, int]):

traits-stubs/traits_stubs_tests/examples/Any.py

@@ -52,9 +52,8 @@ class Foo:
 
 class Superclass(HasTraits):
     x = Any()
-    # y = Any()
 
 
 class Subclass(Superclass):
-    x = Instance(Foo)
+    x = Instance(Foo)  # E: assignment
     y = Int()

traits/tests/test_any.py

@@ -19,6 +19,13 @@
 
 
 class TestAny(unittest.TestCase):
+    def test_default_default(self):
+        class A(HasTraits):
+            foo = Any()
+
+        a = A()
+        self.assertEqual(a.foo, None)
+
     def test_list_default(self):
         message_pattern = r"a default value of type 'list'.* will be shared"
         with self.assertWarnsRegex(DeprecationWarning, message_pattern):
@@ -50,3 +57,40 @@ class A(HasTraits):
         a.foo["color"] = "red"
         self.assertEqual(a.foo, {"color": "red"})
         self.assertEqual(b.foo, {})
+
+    def test_with_factory(self):
+        class A(HasTraits):
+            foo = Any(factory=dict)
+
+        a = A()
+        b = A()
+
+        self.assertEqual(a.foo, {})
+        self.assertEqual(b.foo, {})
+
+        # Defaults are not shared.
+        a.foo["key"] = 23
+        self.assertEqual(a.foo, {"key": 23})
+        self.assertEqual(b.foo, {})
+
+        # An assigned dictionary is shared.
+        a.foo = b.foo = {"red": 0xFF0000}
+        a.foo["green"] = 0x00FF00
+        self.assertEqual(b.foo["green"], 0x00FF00)
+
+    def test_with_factory_and_args(self):
+        def factory(*args, **kw):
+            return "received", args, kw
+
+        args = (21, 34, "some string")
+        kw = {"bar": 57}
+
+        class A(HasTraits):
+            foo = Any(factory=factory, args=args, kw=kw)
+
+        a = A()
+        self.assertEqual(a.foo, ("received", args, kw))
+
+    def test_with_default_value_and_factory(self):
+        with self.assertRaises(TypeError):
+            Any(23, factory=int)

traits/trait_types.py

@@ -201,6 +201,13 @@ class Any(TraitType):
             will no longer be copied. If you need a per-instance default, use a
             ``_trait_name_default`` method to supply that default.
 
+    factory : callable, optional
+        A callable, that when called with *args* and
+        *kw*, returns the default value for the trait.
+    args : tuple, optional
+        Positional arguments (if any) for generating the default value.
+    kw : dictionary, optional
+        Keyword arguments (if any) for generating the default value.
     **metadata
         Metadata for the trait.
     """
@@ -214,7 +221,15 @@ class Any(TraitType):
     #: A description of the type of value this trait accepts:
     info_text = "any value"
 
-    def __init__(self, default_value=NoDefaultSpecified, **metadata):
+    def __init__(
+        self,
+        default_value=NoDefaultSpecified,
+        *,
+        factory=None,
+        args=(),
+        kw={},
+        **metadata
+    ):
         if isinstance(default_value, list):
             warnings.warn(
                 (
@@ -240,6 +255,17 @@ def __init__(self, default_value=NoDefaultSpecified, **metadata):
             )
             self.default_value_type = DefaultValue.dict_copy
 
+        # Sanity check the parameters
+        if default_value is not NoDefaultSpecified and factory is not None:
+            raise TypeError(
+                "ambiguous defaults: both a default value and a default "
+                "value factory are specified"
+            )
+
+        if factory is not None:
+            self.default_value_type = DefaultValue.callable_and_args
+            default_value = (factory, args, kw)
+
         super().__init__(default_value, **metadata)