added solution 4

solutions/Day-1/solution-4.py

+import random
+
+
+class ShapeFactory:
+    factories = {}
+
+    @staticmethod
+    def add_factory(shape_id, shape_factory):
+        assert issubclass(shape_factory, FactoryCreatable), "Not creatable!"  # we test that this is the right type
+        ShapeFactory.factories[shape_id] = shape_factory.create  # we know that it has a create
+
+    @staticmethod
+    def create_shape(id):
+        shape_id = id.__name__  # class name as id
+        if id not in ShapeFactory.factories.keys():
+            ShapeFactory.add_factory(shape_id, id)  # we pass in the class again
+        return ShapeFactory.factories[shape_id]()  # we can simply call it with ()
+
+
+class Shape(object):
+    pass
+
+
+class FactoryCreatable:
+    @classmethod
+    def create(cls):
+        return cls()
+
+
+class Circle(Shape, FactoryCreatable):
+    def draw(self):
+        print("Circle.draw")
+
+    def erase(self):
+        print("Circle.erase")
+
+
+class Square(Shape, FactoryCreatable):
+    def draw(self):
+        print("Square.draw")
+
+    def erase(self):
+        print("Square.erase")
+
+
+class Triangle(Shape, FactoryCreatable):
+    def draw(self):
+        print("Triangle.draw")
+
+    def erase(self):
+        print("Triangle.erase")
+
+
+# what follows is the client code, we want to randomly create shape type objects
+
+def shape_name_gen(n):
+    types = Shape.__subclasses__()
+    for i in range(n):
+        yield random.choice(types)  # NOTE: We now pass in the Shape sub-class itself
+
+
+shapes = [ShapeFactory.create_shape(i)
+          for i in shape_name_gen(5)]
+
+for shape in shapes:
+    shape.draw()
+    shape.erase()