In a previous article, we discussed how to use the strategy pattern to dynamically change an object’s behavior at runtime. Classically, polymorphism in object-oriented design is static and achieved through inheritance; however, with the strategy pattern you can accomplish the same goal dynamically. Indeed, this is an excellent way to handle situations when you need an object to exhibit different behavior at different times. However, it’s worth noting that the strategy pattern requires mutation of the object you’re working with. By using the strategy pattern, you are necessarily changing the algorithm that an object uses for a given behavior. In some situations, it may be preferable not to mutate a given object. Or more likely, you won’t even have the option of mutating an object because it may come from a codebase over which you have no control (such as an external library). Such cases are relatively common; however, it’s still possible to enhance an immutable object’s behavior. One effective means to do so is with the decorator pattern.
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I have been a Raoul Dufy fan for over ten years, searching out his paintings throughout museums in the US. I've been looking for information about him but come up empty. Found this dvd on Amazon. It was great. The documentary had terrific interviews and gorgeous images of his paintings. Even more it gave me a baseline for who is was and the scope of his work.
Now, assume one also desires the ability to add borders to windows. Again, the original Window class has no support. The ScrollingWindow subclass now poses a problem, because it has effectively created a new kind of window. If one wishes to add border support to many but not all windows, one must create subclasses WindowWithBorder and ScrollingWindowWithBorder etc. This problem gets worse with every new feature or window subtype to be added. For the decorator solution, we simply create a new BorderedWindowDecorator—at runtime, we can decorate existing windows with the ScrollingWindowDecorator or the BorderedWindowDecorator or both, as we see fit. Notice that if the functionality needs to be added to all Windows, you could modify the base class and that will do. On the other hand, sometimes (e.g., using external frameworks) it is not possible, legal, or convenient to modify the base class.
Heller’s protagonist, Jim Stegner, is an unschooled but talented painter who struggles with drink, with womanizing, and with his temper. These traits have led him to be a killer, although Heller goes to great pains to let us know these acts are not premeditated. They’ve also, in accordance with these United States’ innate streak of violence, allowed him to be a cult figure - a talent around whom one feels it necessary to walk on eggshells. (For what it’s worth, this trait is to this reader and social observer the cause of a hollowness within the national psyche.) Stegner wants atonement for his acts, but he doesn’t know how to go about that. So Heller must allow Stegner to be the subject of retributive violence, which allows the painter, as might happen to a pre-adolescent child, to have atonement forced on him. Stegner is as a person and as a literary creation, a mess. Perhaps Heller intends him to be a faux Hemingway: hard drinking, bullying and a crybaby when those tables are turned on him. Stegner doesn’t seem to have the backbone about which an anti-hero’s fatal flaws can be built, though; he’s too much at the whims of fate for that. Heller tries to create philosophical depth for Stegner, but these attempts ring hollow. What he has created in Stegner, however, is a depiction of an instinctive artist, something the American psyche always seeks: talent and success untrammeled by subjecting that psyche to training and the lessons of culture and history. That Stegner is, in the end, a talented but pitiful figure, should tell the reader something very important: instinct that refuses at least a small measure of acculturation eventually become debased.

Modifying classes in this fashion is also possible, though the benefits are not as immediately apparent. Almost certainly, anything which could be done with class decorators could be done using metaclasses, but using metaclasses is sufficiently obscure that there is some attraction to having an easier way to make simple modifications to classes. For Python 2.4, only function/method decorators are being added.
The container must inject a delegate object to the delegate injection point. The delegate object implements the delegate type and delegates method invocations to remaining uninvoked decorators and eventually to the bean. When the container calls a decorator during business method interception, the decorator may invoke any method of the delegate object.
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Now, assume one also desires the ability to add borders to windows. Again, the original Window class has no support. The ScrollingWindow subclass now poses a problem, because it has effectively created a new kind of window. If one wishes to add border support to many but not all windows, one must create subclasses WindowWithBorder and ScrollingWindowWithBorder etc. This problem gets worse with every new feature or window subtype to be added. For the decorator solution, we simply create a new BorderedWindowDecorator—at runtime, we can decorate existing windows with the ScrollingWindowDecorator or the BorderedWindowDecorator or both, as we see fit. Notice that if the functionality needs to be added to all Windows, you could modify the base class and that will do. On the other hand, sometimes (e.g., using external frameworks) it is not possible, legal, or convenient to modify the base class.
Here we ensure that the key student_id is part of the request. Although this validation works, it really does not belong in the function itself. Plus, perhaps there are other routes that use the exact same validation. So, let’s keep it DRY and abstract out any unnecessary logic with a decorator. The following @validate_json decorator will do the job:
Now we have our logit decorator in production, but when some parts of our application are considered critical, failure might be something that needs more immediate attention. Let’s say sometimes you want to just log to a file. Other times you want an email sent, so the problem is brought to your attention, and still keep a log for your own records. This is a case for using inheritence, but so far we’ve only seen functions being used to build decorators.
Concrete Decorator: Here we have two concrete decorators, ExcitedMessageDecorator and QuizzicalMessageDecorator, each of which descends from the abstract MessageDecorator class. However, these decorators do have special behavior in that they override the GetMessage and PrintMessage behaviors and enhance them by calling the base version from MessageDecorator (which in turn delegates to the relevant IMessage object) and then appending exclamations.
And for the more subtle decorators, there a slew of super-cute displays that are much more low-key. Check out these meddling mice, a simple trick or treat text, or this tribute to Edgar Allan Poe. — Jennifer Aldrich, Country Living, "These Halloween Stair Decals Will Instantly Transform Your Home Into a Haunted House," 7 Oct. 2018 Another fun tidbit for all of you aspiring IRL dorm decorators, Hailey painted all the art featured in her freshman dorm — now, that’s the perfect personal touch. — Katelyn Chef, Teen Vogue, "University of Mississippi Dorm Decor," 23 Aug. 2018 We reporters and bloggers eat family style, at a long table chosen and donated by Rachael Ray (and her decorator). — Grant Cornett, Vogue, "The Rise of Refugee Cuisine—a Food-World Trend to Feel Good About," 17 Aug. 2018 The social media sensation has forced some decorators to think outside the box and get creative with non-edible decorations. — Caroline Judelson, Fox News, "Engagement cookies are the new bridal trend," 9 Aug. 2018 The project took Kime two years, during which time decorator and client became close friends. — David Usborne, Town & Country, "The Mysterious Case of the Parnham House Fire," 29 May 2018 The look, which also can be seen in her other homes, reflects the influence of Gail Melikian, Ms. Rafaelian’s best friend and decorator who owns an antique store in Cranston. — Candace Taylor, WSJ, "Inside the Many, Many Homes of This Jewelry Billionaire," 12 July 2018 Naturally, faux fur also appeals to home decorators who want to stay animal-friendly. — Kelsey Kloss, ELLE Decor, "How To Decorate With Faux Fur, According To Top Designers," 7 Sep. 2016 The 11,821 square feet of living space was designed by former White House decorator Michael Smith and features reclaimed fireplace mantels, hand-hewn hardwood floors and custom ironwork. — Jack Flemming, latimes.com, "Mega-producer Jerry Bruckheimer pulls in $11.5 million for Brentwood estate," 16 June 2018

The .__init__() method must store a reference to the function and can do any other necessary initialization. The .__call__() method will be called instead of the decorated function. It does essentially the same thing as the wrapper() function in our earlier examples. Note that you need to use the functools.update_wrapper() function instead of @functools.wraps.
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