Python Design Patterns II(Chapter 9 of Python 3 Object Oriented Programming)

时间：2010-09-05 来源：Ray Z

flyweight >>> import weakref
>>> class CarModel:
    _models = weakref.WeakValueDictionary()
    def __new__(cls, model_name, *args, **kwargs):
        model = cls._models.get(model_name)
        if not model:
            model = super().__new__(cls)
            cls._models[model_name] = model
        return model
    def __init__(self, model_name, air=False, tilt=False,
             cruise_control=False, power_locks=False,
             alloy_wheels=False, usb_charger=False):
        if not hasattr(self, "initted"):
            self.model_name = model_name
            self.air = air
            self.tilt = tilt
            self.cruise_control = cruise_control
            self.power_locks = power_locks
            self.alloy_wheels = alloy_wheels
            self.usb_charger = usb_charger
            self.initted = True
    def check_serial(self, serial_number):
        print("Sorry, we are unable to check "
              "the serial number {0} on the {1} "
              "at this time".format(serial_number, self.model_name))


>>> class Car:
    def __init__(self, model, color, serial):
        self.model = model
        self.color = color
        self.serial = serial
    def check_serial(self):
        return self.model.check_serial(self.serial)


>>> dx = CarModel("FIT DX")
>>> lx = CarModel("FIT LX", air=True, cruise_control=True, power_locks=True, tilt=True)
>>> car1 = Car(dx, "blue", "12345")
>>> car2 = Car(dx, "black", "12346")
>>> car3 = Car(lx, "red", "12347")
>>> id(lx)
20634736
>>> del lx
>>> del car3
>>> import gc
>>> gc.collect()
0
>>> lx = CarModel("FIT LX", air=True, cruise_control=True, power_locks=True, tilt=True)
>>> id(lx)
20634224

command 1 >>> class Window:
2     def exit(self):
3         sys.exit(0)
4
5 >>> class Document:
6     def __init__(self, filename):
7         self.filename = filename
8         self.contents = "This file cannot be modified"
9     def save(self):
10         with open(self.filename, 'w') as file:
11             file.write(self.contents)
12
13
14 >>> class ToolbarButton:
15     def __init__(self, name, iconname):
16         self.name = name
17         self.iconname = iconname
18     def click(self):
19         self.command.execute()
20
21
22 >>> class MenuItem:
23     def __init__(self, menu_name, menuitem_name):
24         self.menu = menu_name
25         self.item = menuitem_name
26     def click(self):
27         self.command.execute()
28
29
30 >>> class KeyboardShortcut:
31     def __init__(self, key, modifier):
32         self.key = key
33         self.modifier = modifier
34     def keypress(self):
35         self.command.execute()
36
37
38 >>> class SaveCommand:
39     def __init__(self, document):
40         self.document = document
41     def execute(self):
42         self.document.save()
43
44
45 >>> class ExitCommand:
46     def __init__(self, window):
47         self.window = window
48     def execute(self):
49         self.window.exit()
50
51 >>> window = Window()
52 >>> document = Document("c:\\1.txt")
53 >>> save = SaveCommand(document)
54 >>> exit = ExitCommand(window)
55 >>> save_button = ToolbarButton('save', 'save.png')
56 >>> save_button.command = save
57 >>> save_keystroke = KeyboardShortcut('s', 'ctrl')
58 >>> save_keystroke.command = save
59 >>> exit_menu = MenuItem("File", "Exit")
60 >>> exit_menu.command = exit