当出现以下几种情况时，可以考虑使用构造模式：
- 当想要创建一个复杂对象(对象由多个部分构成，且对象的创建要经过多个不同的步骤，这些步骤也许还遵从特定的顺序)
- 要求一个对象能有不同的表现，并希望将对象的构造与表现解耦
- 想要在某个时间点创建对象，但在稍后的时间点再访问
可以这么理解，你要买电脑，工厂模式直接返回一个你需要型号的电脑，但是构造模式允许你自定义电脑各种配置类型，组装完成后给你。这个过程你可以传入builder从而自定义创建的方式。
方式一
class Computer:
def __init__(self, serial_number):
self.serial_number = serial_number
self.memory = None
self.hdd = None
self.gpu = None
def __str__(self):
info = ('Memory: {}GB'.format(self.memory),
'Hard Disk: {}GB'.format(self.hdd),
'Graphics Card: {}'.format(self.gpu))
return '\n'.join(info)
class ComputerBuilder:
def __init__(self):
self.computer = Computer('AG23385193')
def configure_memory(self, memory):
self.computer.memory = memory
def configure_hdd(self, amount):
self.computer.hdd = amount
def configure_gpu(self, gpu_model):
self.computer.gpu = gpu_model
class HardwareEngineer:
def __init__(self):
self.builder = None
def construct_computer(self, memory, hdd, gpu):
self.builder = ComputerBuilder()
[step for step in (self.builder.configure_memory(memory),
self.builder.configure_hdd(hdd),
self.builder.configure_gpu(gpu))]
@property
def computer(self):
return self.builder.computer
def main():
# 使用buidler，可以创建多个builder类实现不同的组装方式
engineer = HardwareEngineer()
engineer.construct_computer(hdd=500, memory=8, gpu='GeForce GTX 650 Ti')
computer = engineer.computer
print(computer)
if __name__ == '__main__':
main()
方式二
这种方式以前在 Android 开发使用 Retrofit 库时使用过，这是一种链式调用。
class Computer:
def __init__(self, builder):
self.serial_number = builder.serial_number
self.memory = builder.memory
self.hdd = builder.hdd
self.gpu = builder.gpu
def __str__(self):
info = ('Memory: {}GB'.format(self.memory),
'Hard Disk: {}GB'.format(self.hdd),
'Graphics Card: {}'.format(self.gpu))
return '\n'.join(info)
class ComputerBuilder:
def __init__(self):
self.serial_number = None
self.memory = None
self.hdd = None
self.gpu = None
def configure_serial_number(self, serial_number):
self.serial_number = serial_number
return self
def configure_memory(self, memory):
self.memory = memory
return self
def configure_hdd(self, amount):
self.hdd = amount
return self
def configure_gpu(self, gpu_model):
self.gpu = gpu_model
return self
def build(self):
return Computer(self)
def main():
computer = (Computer.ComputerBuilder()
.configure_serial_number('AG23385193')
.configure_memory(8)
.configure_hdd(500)
.configure_gpu('GeForce GTX 650 Ti')
.build())
print(computer)
if __name__ == '__main__':
main()