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.
Oil painting is the process of painting with pigments that are bound with a medium of drying oil, such as linseed oil, which was widely used in early modern Europe. Often the oil was boiled with a resin such as pine resin or even frankincense; these were called 'varnishes' and were prized for their body and gloss. Oil paint eventually became the principal medium used for creating artworks as its advantages became widely known. The transition began with Early Netherlandish painting in northern Europe, and by the height of the Renaissance oil painting techniques had almost completely replaced tempera paints in the majority of Europe.
Decorator Abstractions: Our decorator abstraction takes the form of the abstract MessageDecorator class, which also implements IMessage. The MessageDecorator class has a constructor that accepts an IMessage object as a parameter and then assigns it to a private variable. For its part, MessageDecorator doesn’t have any special behaviors and simply delegates GetMessage and PrintMessage calls to whichever IMessage object was injected into it.
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Enforcement of this Act by the Painter-Stainers Company was sought up until the early 19th century, with master painters gathering irregularly to decide the fees that a journeyman could charge, and also instigating an early version of a job centre in 1769, advertising in the London newspapers a "house of call" system to advertise for journeymen and also for journeymen to advertise for work. The guild's power in setting the fee a journeyman could charge was eventually overturned by law in 1827, and the period after this saw the guild's power diminish, along with that of the other guilds; the guilds were superseded by trade unions, with the Operative United Painters' Union forming sometime around 1831.[2]

Did you get it? We just applied the previously learned principles. This is exactly what the decorators do in Python! They wrap a function and modify its behaviour in one way or the another. Now you might be wondering that we did not use the @ anywhere in our code? That is just a short way of making up a decorated function. Here is how we could have run the previous code sample using @.
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