The builder pattern

builder.py

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+#!/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()
+
+    Write Preview 
+
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