Python 设计模式: 建造者模式(builder pattern)

当一个对象必须经过多个步骤来创建，并且要求不同的参数可以产生不同的表现的时候， 我们可以使用建造者模式。

比如下面这个摘自《Mastering Python Design Patterns》 的例子:

class Computer:
    def __init__(self, serial_number):
        self.serial = serial_number
        self.memory = None
        self.cpu = None
        self.disk = None


    def __str__(self):
        return 'memory: {0} GB, cpu: {1}, disk: {2} GB'.format(
            self.memory, self.cpu, self.disk
        )


class ComputerBuilder:
    def __init__(self):
        self.computer = Computer('SN-12345555')

    def configure_memory(self, memory):
        self.computer.memory = memory

    def configure_cpu(self, cpu):
        self.computer.cpu = cpu

    def configure_disk(self, disk):
        self.computer.disk = disk


class HardwareEngineer:
    def __init__(self):
        self.builder = None

    def construct_computer(self, memory, cpu, disk):
        self.builder = ComputerBuilder()
        self.builder.configure_memory(memory)
        self.builder.configure_cpu(cpu)
        self.builder.configure_disk(disk)

    @property
    def computer(self):
        return self.builder.computer

engineer = HardwareEngineer()
engineer.construct_computer(16, 8, 500)
computer = engineer.computer
print(computer)

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