To calculate the tenth Fibonacci number, you should really only need to calculate the preceding Fibonacci numbers, but this implementation somehow needs a whopping 177 calculations. It gets worse quickly: 21891 calculations are needed for fibonacci(20) and almost 2.7 million calculations for the 30th number. This is because the code keeps recalculating Fibonacci numbers that are already known.
The decorator pattern, also known as the wrapper pattern, is when you wrap an object within another object, thus providing a means of enhancing or overriding certain behavior. The wrapper object will delegate any incoming method calls to the original object, unless it defines a new method to enhance or replace the original object’s behavior. By using the decorator pattern, you can dynamically create as many decorated objects as you want, each enhancing the behavior of the original object in a unique way — and all without mutating the original object. In this manner, you can effectively add, remove, or extend behaviors at runtime.
In Python 2.4a3 (to be released this Thursday), everything remains as currently in CVS. For 2.4b1, I will consider a change of @ to some other single character, even though I think that @ has the advantage of being the same character used by a similar feature in Java. It's been argued that it's not quite the same, since @ in Java is used for attributes that don't change semantics. But Python's dynamic nature makes that its syntactic elements never mean quite the same thing as similar constructs in other languages, and there is definitely significant overlap. Regarding the impact on 3rd party tools: IPython's author doesn't think there's going to be much impact; Leo's author has said that Leo will survive (although it will cause him and his users some transitional pain). I actually expect that picking a character that's already used elsewhere in Python's syntax might be harder for external tools to adapt to, since parsing will have to be more subtle in that case. But I'm frankly undecided, so there's some wiggle room here. I don't want to consider further syntactic alternatives at this point: the buck has to stop at some point, everyone has had their say, and the show must go on.
The decorator pattern is a design pattern that allows you to wrap an object such that it will appear to execute a given behavior in many different ways at different points in program execution. This is especially useful when you want an object to have different behaviors at but are unable to mutate the object. The decorator pattern is a useful way to implement dynamic behavior without needing an extended inheritance-based class hierarchy. To use the decorator pattern you need four elements: a component interface; a concrete component; a decorator abstraction; and, a concrete decorator. The interface sets the contract for both component and decorator behavior, the decorator abstraction contains a pointer to some concrete component, and the concrete decorators wrap a concrete component and override behavior if desired.
Gouache is a water-based paint consisting of pigment and other materials designed to be used in an opaque painting method. Gouache differs from watercolor in that the particles are larger, the ratio of pigment to water is much higher, and an additional, inert, white pigment such as chalk is also present. This makes gouache heavier and more opaque, with greater reflective qualities. Like all watermedia, it is diluted with water.[21]
Component Interface: The component interface is an abstraction describing the behaviors of the components that you will eventually use in your program. Any objects that will use these components will do so through the interface, meaning that they are principally concerned with the abstraction (not the actual object). This is what allows both objects and wrapped objects to be considered to be the same type.
The decorate() proposal was that no new syntax be implemented -- instead a magic function that used introspection to manipulate the following function. Both Jp Calderone and Philip Eby produced implementations of functions that did this. Guido was pretty firmly against this -- with no new syntax, the magicness of a function like this is extremely high:
Just take a look at the code again. In the if/else clause we are returning greet and welcome, not greet() and welcome(). Why is that? It’s because when you put a pair of parentheses after it, the function gets executed; whereas if you don’t put parenthesis after it, then it can be passed around and can be assigned to other variables without executing it. Did you get it? Let me explain it in a little bit more detail. When we write a = hi(), hi() gets executed and because the name is yasoob by default, the function greet is returned. If we change the statement to a = hi(name = "ali") then the welcome function will be returned. We can also do print hi()() which outputs now you are in the greet() function.
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The invention of photography had a major impact on painting. In the decades after the first photograph was produced in 1829, photographic processes improved and became more widely practiced, depriving painting of much of its historic purpose to provide an accurate record of the observable world. A series of art movements in the late 19th and early 20th centuries—notably Impressionism, Post-Impressionism, Fauvism, Expressionism, Cubism, and Dadaism—challenged the Renaissance view of the world. Eastern and African painting, however, continued a long history of stylization and did not undergo an equivalent transformation at the same time.[citation needed]