Comments on: Six GoF design patterns, Python style

By: Max Guernsey, III

Max Guernsey, III — Tue, 12 Jul 2011 19:06:30 +0000

Your decorator example is not a decorator pattern. Decorator patterns encapsulate variations in behavior over time by allowing you to dynamically add and/or remove them (usually add). I think if you switched to a lambda, you’d be okay calling that a decorator.

Also the iterator pattern example doesn’t do a lot for me. Why not show how to make a newly iterable thing – which is the interesting part – rather than iterate over something like an array or a dictionary – which is the part most people could probably have guessed for themselves.

The other four are concise, informative, and correct.

By: Spinner

Spinner — Thu, 11 Nov 2010 23:22:26 +0000

How about this for Python style State Pattern

import EasyStatePattern as esp
class StateContext( esp.ContextBase):

	ttable = esp.TransitionTable('myState')

	def __init__(self):
		StateContext.ttable.initialize(self)

	@esp.transitionevent(ttable)
	def writeName(self, name):
		pass

class StateA(StateContext):

	def writeName(self, name):
		print name.lower()

class StateB(StateContext):

	def writeName(self, name):
		print name.upper()

class StateC(StateB):
	pass

# Set up transition table to cause states totoggle
StateContext.ttable.nextStates(StateA, (StateB,))
StateContext.ttable.nextStates(StateB, (StateC,))
StateContext.ttable.nextStates(StateC, (StateA,))
StateContext.ttable.initialstate = StateA


if __name__=='__main__':
   ctxt = StateContext()
   ctxt.writeName("Monday")
   ctxt.writeName("Tuesday")
   ctxt.writeName("Wednesday")
   ctxt.writeName("Thursday")
   ctxt.writeName("Friday")
   ctxt.writeName("Saturday")
   ctxt.writeName("Sunday")
   x = raw_input("done>")

By: Ryan Ginstrom

Ryan Ginstrom — Tue, 17 Mar 2009 02:41:23 +0000

@Stu

That’s a good point. Metaclasses are certainly very powerful, but they’re also complex and harder.

By: Stu

Stu — Mon, 16 Mar 2009 18:14:28 +0000

I wonder if the factory stuff is worth doing with metaclasses (I’m new to metaclasses, so might be talking rubbish).

By: -= Linkage: 2007.10.11 =-

-= Linkage: 2007.10.11 =- — Mon, 26 Jan 2009 15:43:13 +0000

[...] PyGoF
[...]

By: Tech Messages | 2008-07-02 | Slaptijack

Tech Messages | 2008-07-02 | Slaptijack — Fri, 25 Jul 2008 06:56:32 +0000

[...] The GITS Blog » Six GoF design patterns, Python styleDesign patterns in Python. [...]

By: Jeff

Jeff — Fri, 11 Jul 2008 21:15:52 +0000

Thanks a bunch for this.

By: lvs

lvs — Wed, 17 Oct 2007 01:46:29 +0000

THX
very good article

By: Ryan Ginstrom

Ryan Ginstrom — Tue, 09 Oct 2007 23:29:39 +0000

@David

You’re right that the abstract factory is a bit off. I think that in a “pure” version, I’d return a DogFactory or a CatFactory, then in the PetShop class, do
pet = self.pet_factory.get_pet()
food = self.pet_factory.get_food()
…

However, all I needed was a pet, and not a family of classes, so I fudged. But I can see how that would confuse the issue, so I’ve edited the code to show the “pure” pattern. What do you think?

By: Ryan Ginstrom

Ryan Ginstrom — Tue, 09 Oct 2007 23:27:33 +0000

“In the factory example did the parrot input gave an error in the Japanese translation and thus it was only echoed?”

The idea was to fail gracefully. Failure to find a translation shouldn’t crash your program. And instead of checking for the msgid in the dictionary, it assumes it’s there, then deals with the error if it’s not (BTAFTP)…

The reason I did Unicode was that in real life(TM), I’d imagine the translation dictionary stored on disk in utf-8, then have the strings converted to Unicode for display on screen.