Question

如何将两个功能组合在一起

我有一个控制某些硬件的类：

class Heater()
    def set_power(self,dutycycle, period)
       ...
    def turn_on(self)
       ...
    def turn_off(self)

一个连接数据库并处理实验的所有数据记录功能的类：

class DataLogger()
    def __init__(self)
        # Record measurements and controls in a database
    def start(self,t)
        # Starts a new thread to acquire and record measuements every t seconds

现在，在我的程序recipe.py中，我想做类似的事情：

        log = DataLogger()

        @DataLogger_decorator
        H1 = Heater()

        log.start(60)

        H1.set_power(10,100)
        H1.turn_on()
        sleep(10)
        H1.turn_off()
        etc

数据记录器记录H1上的所有操作。我可以改变所涉及的任何类，只是寻找一种优雅的方式来做到这一点。理想情况下，硬件功能与数据库和DataLogger功能保持分离。理想情况下，DataLogger可重复用于其他控件和测量。

Answer 1

对于这种情况，我更喜欢使用DataLogger作为BaseClass或Mixin用于其他类，而不是尝试做某种装饰魔术（它并没有真正点击我作为使用装饰器的pythonic方式）

e.g：

class DataLogger(object):
  def __init__(self):
      # do init stuff

  def startlog(self, t):
      # start the log 


class Heater(DataLogger):
   def __init__(self):
      # do some stuff before initing your dataLogger
      super(Heater, self).__init__() # init the DataLogger
   #other functions

你可以这样做：

h1 = Heater()
h1.startlog(5)
h1.do_other_stuff()

将其用作现有类的mixin的示例：

class DataLoggerMixin(object): 
  def __init__(self):
    # do your init things
    super(DataLogger, this).__init__()  # this will trigger the next __init__ call in the inheritance chain (i.e. whatever you mix it with)

class Heater(object):
    """ Here's a heater you have lying around that doesn't do data logging.  No need to change it."""

# add a new child class with 2 lines, that includes the DataLoggerMixin as the first parent class, and you will have a new class with all the DataLogging functionality and the Heater functionality. 
class LoggingHeater(DataLoggerMixin, Heater):
    """ Now its a data logging heater """
    pass  # no further code should be necessary if you list DataLoggerMixin first in the base classes. 


>>> logging_heater = LoggingHeater()
>>> logging_heater.start_log(5)
>>> logging_heater.do_heater_stuff()

在python中成功使用mixins的关键是理解方法解析顺序（MRO），特别是对于super，在多重继承情况下是如何工作的。有关合作多重继承，请参阅this。

____________________________________________________________________

替代方法：使用包装类

如果Mixin方法不适用于您的方案，另一种选择是使用DataLogger作为要记录的对象的包装类。基本上，Data Logger会接受一个对象来在其构造函数中进行登录，如下所示：

class DataLogger(object)
  def __init__(self, object_to_log)
    self.object = object_to_log   # now you have access to self.object in all your methods.
    # Record measurements and controls in a database
  def start(self,t)
    # Starts a new thread to aqcuire and reccord measuements every t secconds

我不确定执行了什么类型的日志记录或监视，以及您是否需要访问要记录的对象或它是否独立。如果前者（可能是Heater，Valve等）都实现了DataLogger关心的相同功能，那么无论它们是什么类，您都可以记录它们。（这是像Python这样的动态语言的一个方便的核心功能叫做“Duck typing”，你可以在不同的类型上操作，只要类型实现你关心的功能或属性。“如果它像鸭子一样嘎嘎叫...... “）

您的代码可能看起来更像这样，使用包装类方法：

h1 = Heater() 
log = DataLogger(h1)
log.start(60)
h1.set_power(10,100)
h1.turn_on()
sleep(10)
h1.turn_off()

希望这有帮助！

Answer 2

您可以装饰Heater并将Logger作为装饰器的参数提供：

# define the primitive logger

class Logger(object):
    def log(self, func, args, kwargs):
        print "Logging %s %r %r" % (func, args, kwargs)


# define the decorator
# since it accepts an argument, it's essentially a decorator generator
# which is supposed to return the actual decorator
# which in turn adds a logger call to each method of the class

def with_logger(logger):

    def method_wrapper(cls):

        def wrap(name, fun):
            def _(self, *a, **kw):
                logger.log(name, a, kw)
                return fun(self, *a, **kw)
            return _

        for k in dir(cls):
            v = getattr(cls, k)
            if not k.startswith('__') and callable(v):
                setattr(cls, k, wrap(k, v))
        return cls

    return method_wrapper


# create a logger...

my_logger = Logger()

# ...and pass it to the decorator

@with_logger(my_logger)
class Heater(object):
    def set_power(self,dutycycle, period):
        pass
    def turn_on(self):
        pass
    def turn_off(self):
        pass

# let's test!

h = Heater()
h.set_power(100, 200)
h.turn_on()
h.turn_off()

优雅的方式为以前定义的功能添加功能

如何将两个功能组合在一起

2 个答案: