Factory.create(): Add construct kwarg

docs/rst/usage.rst

@@ -117,6 +117,31 @@ Any subtype of an allowed type is allowed:
     >>> factory.create("lamb", allowed_cls=Sheep)
     Lamb(wool='some')
 
+.. note::
+
+   A very common and Pythonic design pattern consists in defining special
+   constructors using class methods. If you use this approach, *Dessine-moi*
+   lets you select a constructor using the ``construct`` argument. For
+   demonstrative purposes, let us attach a class method constructor to our
+   ``Sheep`` class:
+
+   .. doctest::
+
+      >>> @classmethod
+      ... def unsheavable(cls):
+      ...     return cls(wool="none")
+      >>> Sheep.unsheavable = unsheavable
+
+   We can now route object creation to this function using the ``construct``
+   keyword argument. Since the ``unsheavable()`` class method takes no argument,
+   we do not pass the ``args`` and ``kwargs`` arguments:
+
+   .. doctest::
+
+      >>> factory.create("sheep", construct="unsheavable")
+      Sheep(wool='none')
+
+
 Convert objects
 ^^^^^^^^^^^^^^^
 

src/dessinemoi/__init__.py

@@ -109,6 +109,7 @@ def create(
         self,
         type_id: str,
         allowed_cls: Optional[Union[Type, Tuple[Type]]] = None,
+        construct: Optional[str] = None,
         args: Optional[Sequence] = None,
         kwargs: Optional[MutableMapping] = None,
     ) -> Any:
@@ -123,6 +124,10 @@ def create(
             restricted. If ``type_id`` does not reference one of these allowed
             types, an exception will be raised.
 
+        :param construct:
+            If not ``None``, attempt instantiation using a class method
+            constructor instead of the default constructor.
+
         :param args:
             A sequence of arguments to pass to the constructor of the created
             type.
@@ -153,7 +158,10 @@ def create(
         if kwargs is None:
             kwargs = dict()
 
-        return cls(*args, **kwargs)
+        if construct is not None:
+            return getattr(cls, construct)(*args, **kwargs)
+        else:
+            return cls(*args, **kwargs)
 
     def _convert_impl(
         self,

tests/test_dessinemoi.py

@@ -10,7 +10,7 @@ def factory():
     yield Factory()
 
 
-def test_factory_create(factory):
+def test_factory_instantiate(factory):
     # A Factory instance can be created
     assert isinstance(factory, Factory)
 
@@ -81,6 +81,23 @@ class Ram(Sheep):
         factory.create("sheep", args=(5, "Dolly"), allowed_cls=Ram)
 
 
+def test_factory_classmethod(factory):
+    @factory.register
+    @attr.s(frozen=True)
+    class Sheep:
+        _TYPE_ID = "sheep"
+        age = attr.ib()
+        name = attr.ib()
+
+        @classmethod
+        def old(cls, name):
+            return cls(15, name)
+
+    # The construct parameter allows for the selection of a class method constructor
+    s = factory.create("sheep", construct="old", kwargs={"name": "Romuald"})
+    assert s.age == 15
+
+
 def test_convert(factory):
     @factory.register
     @attr.s(frozen=True)