1class Material:
 2
 3    density = -1
 4
 5    def __init__(self, weight):
 6        self.weight = weight
 7        self.used = False
 8
 9    @property
10    def volume(self):
11        return self.weight / self.density
12
13
14class Concrete(Material):
15
16    density = 2500
17
18
19class Brick(Material):
20
21    density = 2000
22
23
24class Stone(Material):
25
26    density = 1600
27
28
29class Wood(Material):
30
31    density = 600
32
33
34class Steel(Material):
35
36    density = 7700
37
38
39existing_materials = {
40    "Concrete" : Concrete, "Brick" : Brick,
41    "Stone" : Stone, "Wood" : Wood, "Steel" : Steel
42    }
43
44
45class Factory:
46
47    _all_factories = []
48
49    def __init__(self):
50        self.materials_made = []
51        Factory._all_factories.append(self)
52
53    def _create_alloy(self, *args):
54        unique_material_names = []
55        for material in args:
56            unique_material_names.extend(material.__class__.__name__.split("_"))
57        alloy_name = "_".join(sorted(unique_material_names))
58        try:
59            for material in args:
60                material.used = True
61            return existing_materials[alloy_name](sum(material.weight for material in args))
62        except KeyError:
63            density = sum(existing_materials[material_name].density 
64                          for material_name in unique_material_names) / (alloy_name.count("_") + 1)
65            existing_materials[alloy_name] = type(alloy_name, (Material, ), {'density': density})
66            return existing_materials[alloy_name](sum(material.weight for material in args)) 
67         
68    def __call__(self, *args, **kwargs):
69        if not args and not kwargs:
70            raise ValueError("Cannot call Factory without arguments.")
71        if args and kwargs:
72            raise ValueError("Cannot call Factory with both positional and keyword arguments.")  
73        if kwargs:
74            try:
75                materials = []
76                for material, weight in kwargs.items():
77                    materials.append(existing_materials[material](weight))
78            except KeyError:
79                raise ValueError("Incorrect input for materials.")
80            self.materials_made.extend(materials)
81            return tuple(materials)
82        else:
83            if any(material.used for material in args):
84                raise AssertionError("Materials already used.")
85            else:
86                new_alloy = self._create_alloy(*args)
87                self.materials_made.append(new_alloy)
88                return new_alloy
89
90    def can_build(self, target_volume):
91        return sum(material.volume for material in self.materials_made if not material.used) >= target_volume
92
93    @classmethod
94    def can_build_together(cls, target_volume):
95        total_volume = 0
96        for factory in cls._all_factories:
97            total_volume += sum(material.volume for material in factory.materials_made if not material.used)
98        return total_volume >= target_volume