How to use the subprocess module to execute external commands in Python 3.x

How to use the subprocess module to execute external commands in Python 3.x

In Python, we often need to execute system commands, such as running other programs, executing shell commands, etc. Python provides the subprocess module, which allows us to easily call external commands and obtain their output.

This article will introduce how to use the subprocess module in Python 3.x to execute external commands and provide some sample code.

1. Execute external commands through the subprocess.run() function
   The subprocess.run() function is a new function in Python 3.5 and later versions. It is used to run specified external commands.

Here is a simple example that demonstrates how to use the subprocess.run() function to execute an external command and get the output of the command:

import subprocess

# 执行外部命令
result = subprocess.run(['ls', '-l'], capture_output=True, text=True)

# 获取命令的输出
output = result.stdout

# 输出到控制台
print(output) 

In the above code, we use The subprocess.run() function executes the ls -l command. Here we use two parameters to control the execution of the command: capture_output=True means to capture the output of the command into the result object, and text=True means to return the output in text form.

2. Execute external commands through the subprocess.Popen() function
   The subprocess module also provides the Popen class, which is a lower-level interface that can be used to execute more complex commands and control the commands. for finer control of input/output.

The following is an example that demonstrates how to use the subprocess.Popen() function to execute an external command and read the output of the command line by line:

import subprocess

# 执行外部命令
process = subprocess.Popen(['ping', 'www.baidu.com'], stdout=subprocess.PIPE, text=True)

# 逐行读取输出
for line in process.stdout:
    print(line.strip())

In the above code , we used the subprocess.Popen() function to execute the ping www.baidu.com command, and returned the command's output through the stdout pipe. We read the output of the command line by line by traversing the stdout pipe and print it to the console.

It should be noted that when using the Popen class to execute a command, it will not automatically wait for the command to be executed. If you need to wait for the command to be executed, you can use the process.wait() function to achieve this.

3. Execute external commands through the subprocess.call() function
   The subprocess module also provides the call function, which is used to execute external commands and wait for its execution to complete.

The following is an example that demonstrates how to use the subprocess.call() function to execute an external command and get the return code of the command:

import subprocess

# 执行外部命令
return_code = subprocess.call(['git', 'clone', 'https://github.com/username/repo'])

# 输出返回码
print(return_code)

In the above code, we use subprocess The .call() function executes the git clone command and passes the address of the warehouse as a parameter. After executing a command by calling the subprocess.call() function, the program will be blocked until the command is executed.

Here you can get the return code of the command through return_code, and you can judge whether the command was executed successfully based on the return code.

Summary:
Through the subprocess module, we can easily execute external commands in Python and obtain the output and return code of the command. This article introduces three commonly used methods: subprocess.run(), subprocess.Popen() and subprocess.call(). According to different needs, choose the appropriate method to execute external commands.

I hope this article will help you understand how to use the subprocess module to execute external commands in Python 3.x.

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