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.
As an example, consider a window in a windowing system. To allow scrolling of the window's contents, one may wish to add horizontal or vertical scrollbars to it, as appropriate. Assume windows are represented by instances of the Window interface, and assume this class has no functionality for adding scrollbars. One could create a subclass ScrollingWindow that provides them, or create a ScrollingWindowDecorator that adds this functionality to existing Window objects. At this point, either solution would be fine.
Painting is an important form in the visual arts, bringing in elements such as drawing, gesture (as in gestural painting), composition, narration (as in narrative art), or abstraction (as in abstract art). Paintings can be naturalistic and representational (as in a still life or landscape painting), photographic, abstract, narrative, symbolistic (as in Symbolist art), emotive (as in Expressionism), or political in nature (as in Artivism).