Example of `builder' design pattern in Python

builder.py

#!/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()