Detailed explanation of the usage of functions in Python

1. Function definition and basic functions

Yes in PythonosA function provided by the module, whose main function is to run a command in the form of a string and pass it to the operating system shell program. In Python,The syntax is very simple, and its basic form is:

(command)

Where command is a string representing the commands that need to be executed in the operating system. For example, on Windows systems, you can use ("notepad") to open Notepad programs; on Linux or macOS systems, you can use ("ls") to list files and folders in the current directory.

The return value of the function is the exit status code after the command is executed. Normally, if the command is executed successfully, the return value is 0; if the command is executed failed, the return value is a non-0 value. This return value can be used to determine whether the command is successfully executed.

2. The function

(I) Execute system commands

The most direct function is to allow Python programs to execute commands in the operating system. This allows Python programs to interact with the operating system and complete some operations that cannot be directly implemented through the Python standard library. For example, you can use it to perform file operations, system configuration modification, program startup and other tasks.

For example, on a Windows system, you can shut down your computer with the following code:

import os
("shutdown /s /t 1")

In Linux systems, you can use the following code to view the memory usage of the current system:

import os
("free -m")

These operations are implemented by calling the operating system commands, providing a simple and direct way to execute these commands.

(II) Calling external programs

In addition to executing the system's own commands, it can also be used to start external programs. This allows Python programs to interact with other applications to achieve more complex functions. For example, you can use it to start a text editor, a browser, or a graphical interface program.

Here is an example of using a startup browser and opening a specified webpage:

import os
("start ")  # Windows System# or("open ")  # macOS system# or("xdg-open ")  # Linux system

In this way, Python programs can work in conjunction with other applications to achieve richer functionality.

(III) Implement cross-platform functions

Although it performs slightly differently in different operating systems, it can still implement cross-platform functionality to a certain extent. By selecting different commands in the code according to the operating system type, programs that can be run on multiple operating systems can be written.

For example, the following code can open a file based on the operating system type:

import os
import sys

if  == "win32":
    ("start ")
elif  == "darwin":
    ("open ")
else:
    ("xdg-open ")

This code determines the current operating system type and calls the corresponding commands according to different operating system types to open the file. This way, the program can run normally on Windows, macOS, and Linux systems.

III. Use scenarios

(I) File and directory operations

Can be used to perform operations related to files and directories. For example, you can use it to create a directory, delete a file, copy a file, etc.

Here is an example of creating a directory using:

import os
("mkdir example_dir")

On Linux and macOS systems, you can use itTo delete the file:

import os
("rm ")

Although these operations can also be implemented through other Python modules, these tasks can be accomplished more intuitively using them.

(II) System configuration and management

It can also be used to perform some system configuration and management tasks. For example, it can be used to modify system time, update system software packages, install software, etc.

In Linux systems, you can use the following code to update the system package:

import os
("sudo apt update")

On Windows systems, you can use the following code to modify the system time:

import os
("time 14:30")

These operations usually require administrator privileges, but these tasks can be easily accomplished.

(III) Automation script

It is also widely used in automated scripts. For example, you can use it to write a script that automatically executes a series of system commands to complete some complex tasks.

Here is a simple example of an automation script that can automatically back up files in a specified directory:

import os
import datetime

# Get the current timenow = ()
timestamp = ("%Y%m%d%H%M%S")

# Create a backup directorybackup_dir = f"backup_{timestamp}"
(f"mkdir {backup_dir}")

# Copy the file to the backup directory(f"cp -r example_dir/* {backup_dir}/")

This script completes the file backup operation by executing a series of commands. In this way, more complex automation scripts can be written to improve work efficiency.

IV. Limitations and Alternative Solutions

Despite its power, it also has some limitations. First, the execution efficiency is relatively low because it requires calling the operating system's shell program to execute commands. Secondly, it is poor in security and is vulnerable to injection attacks. If the command string contains the user input, it may cause a security vulnerability.

For example, the following code has a security vulnerability:

import os
filename = input("Please enter the file name:")
(f"rm {filename}")

If the user enters something similar to; rm -rf /, it will cause the system file to be deleted, causing serious consequences.

To solve these problems, Python provides other modules and functions as a substitute. For example, the subprocess module provides a more flexible and secure way to execute system commands. The subprocess module can avoid calling shell programs, improve execution efficiency, and also prevent injection attacks.

Here is an example of using the subprocess module to execute commands:

import subprocess

(["ls", "-l"])

Compared with that, the subprocess module is more secure and efficient. It allows developers to call system commands directly without having to go through shell programs. At the same time, the subprocess module also provides more functions, such as obtaining the output of the command, setting the timeout time, etc.

5. Summary

It is a very useful function in Python. It allows Python programs to execute commands in the operating system and implement interaction with the operating system. By doing so, you can complete tasks such as file operation, system configuration, program startup, etc., and you can also write automated scripts to improve work efficiency. However, there are also some limitations, such as low execution efficiency and poor security. Therefore, in actual development, appropriate modules and functions can be selected according to needs to implement the execution of system commands. It is a good choice for some simple needs; and for some complex needs, the subprocess module may be more suitable.

The above is a detailed explanation of the usage of functions in Python. For more information about Python functions, please follow my other related articles!