How to use the subprocess module for subprocess management in Python 3.x

How to use the subprocess module for subprocess management in Python 3.x

Introduction:
In Python programming, we often need to interact with external commands or programs, such as executing system commands and starting other application or call other scripts. Subprocess management refers to the operations of creating, controlling, and communicating with subprocesses in Python programs. Python provides the subprocess module to handle subprocess management, which is a powerful and flexible tool. This article will introduce how to use the subprocess module to create, control and communicate with subprocesses.

1. Creation of subprocess
It is very simple to create a subprocess using the subprocess module. You can create a subprocess object by directly calling the constructor method of the Popen class. The following is a simple sample code:

import subprocess

# 执行一个系统命令，输出结果到标准输出
subprocess.Popen(["ls", "-l"])

In this example, we use the constructor method of the Popen class to create a subprocess object. The parameter passed in is a list, and the first element of the list is the The command to be executed, and subsequent elements are the parameters of the command. The above code will execute the system command ls -l and output the results to standard output.

In addition to the above methods, we can also execute Shell commands by specifying the parameter shell=True when creating the subprocess object. The sample code is as follows:

import subprocess

# 执行一个 Shell 命令
subprocess.Popen("ls -l", shell=True)

In the above code, we pass the Shell command "ls -l" as a parameter to the constructor of the Popen class, and pass the parameter shell=True to execute Shell commands.

2. Control of subprocess
After the subprocess is successfully created, we can use various methods of the subprocess object to control the behavior of the subprocess. The following are some commonly used methods:

1. wait(): Wait for the child process to end and return a status code.
2. communicate(input=None): Interact with the child process, you can send content to the child process, and you can also obtain the output results of the child process.
3. poll(): Check whether the child process ends. If it ends, it returns the status code of the process. If it does not end, it returns None.

The following is a sample code that gets the output result and outputs it when the child process ends:

import subprocess

# 执行一个系统命令，获取输出结果
p = subprocess.Popen(["ls", "-l"], stdout=subprocess.PIPE)
output, error = p.communicate()
print(output.decode("utf-8"))

In the above code, we use the communicate() method Interact with the child process, obtain the output result of the child process and assign it to the variable output. Then use the decode("utf-8") method to convert the binary string into a UTF-8 encoded string and print the output.

3. Communication of sub-processes
Using the communicate() method can easily communicate with the sub-process. It can not only send data to the sub-process, but also receive data from the sub-process. Output results. The following is a sample code:

import subprocess

# 执行一个命令并接收子进程的输出
p = subprocess.Popen(["ls", "-l"], stdout=subprocess.PIPE)
output, error = p.communicate()
print(output.decode("utf-8"))

# 向子进程发送数据并接收输出结果
p = subprocess.Popen(["grep", "example"], stdout=subprocess.PIPE, stdin=subprocess.PIPE)
input_data = "This is an example"
output, error = p.communicate(input=input_data.encode("utf-8"))
print(output.decode("utf-8"))

In the above code, we first create a child process object p, execute the command ls -l and output the result to output in. Next, we create a child process object p again, execute the command grep example and send input_data to the child process. Finally, we print the results.

Summary:
By using the subprocess module, we can easily create, control and communicate with subprocesses. In the actual programming process, we can flexibly use these functions according to specific needs to achieve more complex sub-process management operations. I hope this article has been helpful for you to use the subprocess module for subprocess management in Python.

The above is the detailed content of How to use the subprocess module for subprocess management in Python 3.x. For more information, please follow other related articles on the PHP Chinese website!