Python Design Patterns: Prototype Pattern

The Prototype design pattern helps hide the complexity of instances created by a class. The concept of an existing object is different from the concept of a new object, which is created from scratch.

If necessary, the newly copied object may have some changes in its properties. This approach saves time and resources required for product development.

How to Implement the Prototype Pattern

Now let’s see how to implement the Prototype pattern.

import copy

classPrototype:

   _type = None
   _value = None

   def clone(self):
      pass

   def getType(self):
      return self._type

   def getValue(self):
      return self._value

class Type1(Prototype):

   def __init__(self, number):
      self._type = "Type1"
      self._value = number

   def clone(self):
      return copy.copy(self)

class Type2(Prototype):

   """ Concrete prototype. """

   def __init__(self, number):
      self._type = "Type2"
      self._value = number

   def clone(self):
      return copy.copy(self)

class ObjectFactory:

   """ Manages prototypes.
   Static factory, that encapsulates prototype
   initialization and then allows instatiation
   of the classes from these prototypes.
   """

   __type1Value1 = None
   __type1Value2 = None
   __type2Value1 = None
   __type2Value2 = None

   @staticmethod
   def initialize():
      ObjectFactory.__type1Value1 = Type1(1)
      ObjectFactory.__type1Value2 = Type1(2)
      ObjectFactory.__type2Value1 = Type2(1)
      ObjectFactory.__type2Value2 = Type2(2)

   @staticmethod
   def getType1Value1():
      return ObjectFactory.__type1Value1.clone()

   @staticmethod
   def getType1Value2():
      return ObjectFactory.__type1Value2.clone()

   @staticmethod
   def getType2Value1():
      return ObjectFactory.__type2Value1.clone()

   @staticmethod
   def getType2Value2():
      return ObjectFactory.__type2Value2.clone()

def main():
   ObjectFactory.initialize()

   instance = ObjectFactory.getType1Value1()
   print "%s: %s" % (instance.getType(), instance.getValue())

   instance = ObjectFactory.getType1Value2()
   print "%s: %s" % (instance.getType(), instance.getValue())

   instance = ObjectFactory.getType2Value1()
   print "%s: %s" % (instance.getType(), instance.getValue())

   instance = ObjectFactory.getType2Value2()
   print "%s: %s" % (instance.getType(), instance.getValue())

if __name__ == "__main__":
   main()

Output

The above program will produce the following output –

This output helps create new objects from existing ones, as can be clearly seen in the output mentioned above.