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Example of `builder' design pattern in Python
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Example of `builder' 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/>.
class Director:
""" Controls the construction process.
Director has a builder associated with him. Director then
delegates building of the smaller parts to the builder and
assembles them together.
"""
__builder = None
def setBuilder(self, builder):
self.__builder = builder
# The algorithm for assembling a car
def getCar(self):
car = Car()
# First goes the body
body = self.__builder.getBody()
car.setBody(body)
# Then engine
engine = self.__builder.getEngine()
car.setEngine(engine)
# And four wheels
i = 0
while i < 4:
wheel = self.__builder.getWheel()
car.attachWheel(wheel)
i += 1
return car
# The whole product
class Car:
""" The final product.
A car is assembled by the `Director' class from
parts made by `Builder'. Both these classes have
influence on the resulting object.
"""
def __init__(self):
self.__wheels = list()
self.__engine = None
self.__body = None
def setBody(self, body):
self.__body = body
def attachWheel(self, wheel):
self.__wheels.append(wheel)
def setEngine(self, engine):
self.__engine = engine
def specification(self):
print "body: %s" % self.__body.shape
print "engine horsepower: %d" % self.__engine.horsepower
print "tire size: %d\'" % self.__wheels[0].size
class Builder:
""" Creates various parts of a vehicle.
This class is responsible for constructing all
the parts for a vehicle.
"""
def getWheel(self): pass
def getEngine(self): pass
def getBody(self): pass
class JeepBuilder(Builder):
""" Concrete Builder implementation.
This class builds parts for Jeep's SUVs.
"""
def getWheel(self):
wheel = Wheel()
wheel.size = 22
return wheel
def getEngine(self):
engine = Engine()
engine.horsepower = 400
return engine
def getBody(self):
body = Body()
body.shape = "SUV"
return body
class NissanBuilder(Builder):
""" Concrete Builder implementation.
This class builds parts for Nissan's family cars.
"""
def getWheel(self):
wheel = Wheel()
wheel.size = 16
return wheel
def getEngine(self):
engine = Engine()
engine.horsepower = 85
return engine
def getBody(self):
body = Body()
body.shape = "hatchback"
return body
# Car parts
class Wheel:
size = None
class Engine:
horsepower = None
class Body:
shape = None
def main():
jeepBuilder = JeepBuilder()
nissanBuilder = NissanBuilder()
director = Director()
# Build Jeep
print "Jeep"
director.setBuilder(jeepBuilder)
jeep = director.getCar()
jeep.specification()
print ""
# Build Nissan
print "Nissan"
director.setBuilder(nissanBuilder)
nissan = director.getCar()
nissan.specification()
if __name__ == "__main__":
main()
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