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Example of `bridge' design pattern in Python
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Example of `bridge' design pattern
# This code is part of http://wp.me/p1Fz60-8y
# 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 AbstractInterface:
""" Target interface.
This is the target interface, that clients use.
"""
def someFunctionality(self):
raise NotImplemented()
class Bridge(AbstractInterface):
""" Bridge class.
This class forms a bridge between the target
interface and background implementation.
"""
def __init__(self):
self.__implementation = None
class UseCase1(Bridge):
""" Variant of the target interface.
This is a variant of the target Abstract interface.
It can do something little differently and it can
also use various background implementations through
the bridge.
"""
def __init__(self, implementation):
self.__implementation = implementation
def someFunctionality(self):
print "UseCase1: ",
self.__implementation.anotherFunctionality()
class UseCase2(Bridge):
def __init__(self, implementation):
self.__implementation = implementation
def someFunctionality(self):
print "UseCase2: ",
self.__implementation.anotherFunctionality()
class ImplementationInterface:
""" Interface for the background implementation.
This class defines how the Bridge communicates
with various background implementations.
"""
def anotherFunctionality(self):
raise NotImplemented
class Linux(ImplementationInterface):
""" Concrete background implementation.
A variant of background implementation, in this
case for Linux!
"""
def anotherFunctionality(self):
print "Linux!"
class Windows(ImplementationInterface):
def anotherFunctionality(self):
print "Windows."
def main():
linux = Linux()
windows = Windows()
# Couple of variants under a couple
# of operating systems.
useCase = UseCase1(linux)
useCase.someFunctionality()
useCase = UseCase1(windows)
useCase.someFunctionality()
useCase = UseCase2(linux)
useCase.someFunctionality()
useCase = UseCase2(windows)
useCase.someFunctionality()
if __name__ == "__main__":
main()
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