Python in a Nutshell

Functions

Most statements in a typical Python program are organized into functions. A function is a group of statements that executes upon request. Python provides many built-in functions and allows programmers to define their own functions. A request to execute a function is known as a function call. When a function is called, it may be passed arguments that specify data upon which the function performs its computation. In Python, a function always returns a result value, either None or a value that represents the results of its computation. Functions defined within class statements are also called methods. Issues specific to methods are covered in Chapter 5; the general coverage of functions in this section, however, also applies to methods.

In Python, functions are objects (values) and are handled like other objects. Thus, you can pass a function as an argument in a call to another function. Similarly, a function can return another function as the result of a call. A function, just like any other object, can be bound to a variable, an item in a container, or an attribute of an object. Functions can also be keys into a dictionary. For example, if you need to quickly find a function’s inverse given the function, you could define a dictionary whose keys and values are functions and then make the dictionary bidirectional (using some functions from module math, covered in Chapter 15):

inverse = {sin:asin, cos:acos, tan:atan, log:exp} for f in inverse.keys( ): inverse[inverse[f]] ...