Python Notes (3) - Functions

转载请注明出处： http://blog.csdn.net/cxsydjn/article/details/71302965

The note covers funtion syntax, importing modules and build-in functions.

Python notes of open courses @Codecademy.

About Functions

If you need reuse a piece of code, just with a few different values. Instead of rewriting the whole code, it’s much cleaner to define a function, which can then be used repeatedly.

Function Syntax

Function Junction:

Functions are defined with three components:

Header: which includes the def keyword, the name of the function, and any parameters the function requires.Comment: An optional comment that explains what the function does.

Body: which describes the procedures the function carries out. The body is indented, just like for conditional statements.

# Example of a function def hello_world(): """Prints 'Hello World!' to the console.""" print "Hello World!"

Call and Response:

function(parameters)return sthParameters and Arguments: def square(n): n is a parameter of square. A parameter acts as a variable name for a passed in argument. parameter = formal parameter (形参)， argument = actual parameter (实参)。A function can require as many parameters as you’d like, but when you call the function, you should generally pass in a matching number of arguments.Functions Calling Functions A function can call another function, in the way mentioned above.

Importing Modules

A module is a file that contains definitions — including variables and functions — that you can use once it is imported.Generic Imports: import module There is a Python module named math that includes a number of useful variables and functions, and sqrt() is one of those functions. When it’s simply done with the import module and module.function() to access math module in the way below, it’s called a generic import.Function Imports: from module import function Pulling in just a single function from a module is called a function import, and it’s done with the from keyword.

Universal Imports: from module import *

Use the power of from module import * to import everything from the math module.

However, they fill your program with a ton of variable and function names without the safety of those names still being associated with the module(s) they came from.

# Examples of the above importing ways # Generic import import math print math.sqrt(25) # Function import from math import sqrt print sqrt(25) # Universal import from math import * print sqrt(25)

Tips:

A generic import may be the best way.

You may see everything in a module by:

import math # Imports the math module everything = dir(math) # Sets everything to a list of things from math print everything # Prints them all!

Built-in Functions

We may directly use some of the functions that are built in to Python (no modules required!).max(): takes any number of arguments and returns the largest one. min(): returns the smallest of a given series of arguments.abs(): returns the absolute value of the number it takes as an argument—that is, that number’s distance from 0 on an imagined number line. It only takes a single number, unlike max() and min().type(): returns the type of the data it receives as an argument.

External Resources

Functions in PythonFunctions Can Return Something