Syntactic constraints. Python is a syntactically simple language with fairly strong constraints on what can and can't be done without "messing things up" (both visually and with regards to the language parser). There's no obvious way to structure this information so that people new to the concept will think, "Oh yeah, I know what you're doing." The best that seems possible is to keep new users from creating a wildly incorrect mental model of what the syntax means.
When we instantiate a SimpleMessage and then pass it to the various decorators, we now get new behavior. Moreover, since both the concrete component and the concrete decorators all implement / descend from IMessage, they are interchangeable as far as the program is concerned, meaning that we can loop over them together. Further, rather than having to create a new ExcitedAndQuizzicalMessageDecorator class, we were able to achieve the same effect by double wrapping a SimpleMessage object (first in an ExcitedMessageDecorator and then in a QuizzicalMessageDecorator). Finally, note that despite having been passed into various decorators, our simpleMsg object remains unchanged at the end of the program.
Tempera, also known as egg tempera, is a permanent, fast-drying painting medium consisting of colored pigment mixed with a water-soluble binder medium (usually a glutinous material such as egg yolk or some other size). Tempera also refers to the paintings done in this medium. Tempera paintings are very long lasting, and examples from the first centuries CE still exist. Egg tempera was a primary method of painting until after 1500 when it was superseded by the invention of oil painting. A paint commonly called tempera (though it is not) consisting of pigment and glue size is commonly used and referred to by some manufacturers in America as poster paint.
Note that greet_bob(say_hello) refers to two functions, but in different ways: greet_bob() and say_hello. The say_hello function is named without parentheses. This means that only a reference to the function is passed. The function is not executed. The greet_bob() function, on the other hand, is written with parentheses, so it will be called as usual.
Moreover, the use of language is only an abstraction for a color equivalent. The word "red", for example, can cover a wide range of variations from the pure red of the visible spectrum of light. There is not a formalized register of different colors in the way that there is agreement on different notes in music, such as F or C♯. For a painter, color is not simply divided into basic (primary) and derived (complementary or mixed) colors (like red, blue, green, brown, etc.).
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