阿班私房菜-Design Pattern(DP)初探使用Python (1)

最近使用Python 寫程式，心血來潮，使用 (DP) 套用看看。
以 Factory worker 為例。
首先建立一個物件Ｗorker 包含姓名、屬性等等。

class Worker:     def __init__(self, name=None):         self.name = capfirst(name) if name else "The worker"     def getName(self):         return self.name     def attrib(self):        return "Worker"     def lookandfeel(self):         print "%s is a %s" % (self.name, self.attrib())

Designer與Engineer繼承它，並覆寫attrib() Method。

class Designer(Worker):     def attrib(self):        return "Designer" class Engineer(Worker):     def attrib(self):        return "Engineer"

當使用各自物件來建立，並執行lookandfeel() 時，會呼叫各自的attrib method。
以下使用 factory pattern 來實作僱用workers 的容器物件。

# factory pattern class Factory:     type_designer = 1     type_engineer = 2     def __init__(self):         self.workers = []     def employ(self, worker_type, name=None):         if worker_type == Factory.type_designer:             self.workers.append(Designer(name))         elif worker_type == Factory.type_engineer:             self.workers.append(Engineer(name))     def workerCount(self):         return len(self.workers)     def browse(self):         for a in self.workers:             a.lookandfeel() z = Factory() z.employ(Factory.type_designer) z.employ(Factory.type_designer, 'bill') z.employ(Factory.type_engineer, 'sue') z.browse()

執行結果：

$ python factory_dp1.py The worker is a Designer Bill is a Designer Sue is a Engineer

承上篇重構一文：我們來重構一下它，並加入singleton pattern（利用@staticmethod 來實作)。

class Factory:     # class static variable     type_designer = "1"     type_engineer = "2"     _Factoryself = None     _factorydict = {            type_designer: Designer,            type_engineer: Engineer,         }    def __init__(self):         self.workers = []     @staticmethod     def singleton():         if Factory._Factoryself == None:             Factory._Factoryself = Factory()         return Factory._Factoryself     def employ(self, worker_type, name=None):         caller = Factory._factorydict.get(worker_type)         if caller:             self.workers.append(caller(name))         return None     def workerCount(self):         return len(self.workers)     def browse(self):         i = 0         for a in self.workers:             print " - Worker[%s]:%s" % (i, a.getLookandfeel())             i+=1 def main():     f = Factory.singleton()     f2 = Factory.singleton()     if f == f2:         print "* Singleton pattern of Factory"     print "* Factory pattern to employ"     f.employ(Factory.type_designer)     f.employ(Factory.type_designer, 'Bill')     f.employ(Factory.type_engineer, 'Sue')     print "* Factory pattern to browse"     f.browse()     print "* The factory has %s workers." % f.workerCount() if __name__ == "__main__":     main()

小結

使用python 來寫DP程式，功能強大，自由度高；
但這意味，寫其程式時，要有其紀律，遵守一定規範(coding convention)來寫；
不然程式會變得非常難讀及維護。 最近上列範例程式均可在github-class_dp中找到。
上述範例還可進一步，重構或修改為工廠人員管理系統的雛形，留待有興趣的讀者們來添加！