第726页 | Learning Python-Mark Lutz | 阅读 ‧ 电子书库

已读75%
预计阅读本页时间：-

Pocket

Test Your Knowledge: Answers

You can embed a built-in object in a wrapper class, or subclass the built-in type directly. The latter approach tends to be simpler, as most original behavior is automatically inherited.
Function decorators are generally used to add to an existing function a layer of logic that is run each time the function is called. They can be used to log or count calls to a function, check its argument types, and so on. They are also used to “declare” static methods—simple functions in a class that are not passed an instance when called.
New-style classes are coded by inheriting from the object built-in class (or any other built-in type). In Python 3.0, all classes are new-style automatically, so this derivation is not required; in 2.6, classes with this derivation are new-style and those without it are “classic.”
New-style classes search the diamond pattern of multiple inheritance trees differently—they essentially search breadth-first (across), instead of depth-first (up). New-style classes also change the result of the type built-in for instances and classes, do not run generic attribute fetch methods such as __getattr__ for built-in operation methods, and support a set of advanced extra tools including properties, descriptors, and __slots__ instance attribute lists.
Normal (instance) methods receive a self argument (the implied instance), but static methods do not. Static methods are simple functions nested in class objects. To make a method static, it must either be run through a special built-in function or be decorated with decorator syntax. Python 3.0 allows simple functions in a class to be called through the class without this step, but calls through instances still require static method declaration.
Three seconds. (Or, more accurately: “And the Lord spake, saying, ‘First shalt thou take out the Holy Pin. Then, shalt thou count to three, no more, no less. Three shalt be the number thou shalt count, and the number of the counting shall be three. Four shalt thou not count, nor either count thou two, excepting that thou then proceed to three. Five is right out. Once the number three, being the third number, be reached, then lobbest thou thy Holy Hand Grenade of Antioch towards thy foe, who, being naughty in my sight, shall snuff it.’”)^[72]