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Example of `prototype' design pattern in Python
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Example of `prototype' design pattern
# Copyright (C) 2011 Radek Pazdera
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
import copy
class Prototype:
""" Object, that can be cloned.
This is just a base class, so the clone() method
is not implemented. But all subclasses have to
override it.
"""
_type = None
_value = None
def clone(self):
pass
def getType(self):
return self._type
def getValue(self):
return self._value
class Type1(Prototype):
""" Concrete prototype.
Implementation of Prototype. Important part is the
clone() method.
"""
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()
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