Writing and using python modules (example analysis)

In the following article, we will learn about what a python module is. Understand what a python module is, and where and how modules in python can be used in python programming.

Module

Python module (Module) is a Python file, ending with .py, containing Python object definitions and Python statements.

Modules allow you to organize your Python code snippets logically.

Assigning related code to a module can make your code more usable and easier to understand.

Modules can define functions, classes and variables, and modules can also contain executable code.

Python itself has many very useful modules built in. As long as they are installed, these modules can be used immediately.

We take the built-in sys module as an example to write a hello module:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

' a test module '
__author__ = 'Michael wu'
import sys
def test():
    args = sys.argv
    if len(args)==1:
        print('Hello, world!')
    elif len(args)==2:
        print('Hello, %s!' % args[1])
    else:
        print('Too many arguments!')
if __name__=='__main__':
    test()

The 1st and 2nd lines are standard comments. The 1st line of comments can make this hello.py file Run directly on Unix/Linux/Mac, the 2nd line comment indicates that the .py file itself uses standard UTF-8 encoding;

The 4th line is a string indicating the documentation comment of the module, any module code The first string is regarded as the documentation comment of the module;

Line 6 uses the __author__ variable to write the author in, so that others can admire your name when you make the source code public;

The above is the standard file template of the Python module. Of course, you can delete all of them and not write them. However, it is definitely correct to act according to the standards.

The real code part begins at the end.

You may have noticed that the first step to use the sys module is to import the module:

import sys

After importing the sys module, we have the variable sys pointing to the module, using the sys variable , you can access all functions of the sys module.

The sys module has an argv variable, which uses a list to store all the parameters of the command line. argv has at least one element, because the first parameter is always the name of the .py file, for example:

The sys.argv obtained by running python3 hello.py is ['hello.py'];

The sys.argv obtained by running python3 hello.py Michael is ['hello.py', 'Michael].

最后，注意到这两行代码：
if __name__=='__main__':   
 test()

When we run the hello module file on the command line, the Python interpreter sets a special variable __name__ to __main__, and if the hello module is imported elsewhere, the if judgment will fail, so , this if test allows a module to execute some additional code when run through the command line, the most common is to run tests.

We can use the command line to run hello.py to see the effect:

$ python3 hello.py
Hello, world!
$ python hello.py Michael
Hello, Michael!

If you start the Python interactive environment and then import the hello module:

$ python3
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 23 2015, 02:52:03) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import hello
>>>

When importing, Hello is not printed , word!, because the test() function is not executed.

Hello, word! can be printed only when hello.test() is called:

>>> hello.test()
Hello, world!

The above is all the content described in this article. This article mainly introduces the related ## Knowledge of #python module, I hope you can use the information to understand the above content. I hope what I have described in this article will be helpful to you and make it easier for you to learn python.

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