Python Subprocess.popen [In-Depth Guide]

The subprocess.Popen class in Python is a part of the subprocess module, which allows you to create and interact with additional processes. It’s commonly used for running external commands, interacting with their input and output streams, and managing various aspects of those processes. subprocess.Popen is a versatile way to work with external processes.

Here’s a basic example of how to use subprocess.Popen:

import subprocess

# Define the command you want to run as a list of arguments
cmd = ["ls", "-l"]

# Use subprocess.Popen to start the process
process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)

# Communicate with the process and get its output and errors
output, errors = process.communicate()

# Print the output and errors (if any)
print("Output:", output)
print("Errors:", errors)

# Get the return code of the process (0 usually means success)
return_code = process.returncode
print("Return Code:", return_code)
Code language: Python (python)

In this example:

1. We import the subprocess module.
2. Define the command to run as a list of arguments. In this case, we’re running the ls -l command.
3. Use subprocess.Popen to start the process with the specified command. We capture both its standard output (stdout) and standard error (stderr) streams for later use.
4. We use process.communicate() to interact with the process. This method waits for the process to complete and returns the output and error streams.
5. We print the output and errors.
6. We obtain the return code of the process using process.returncode.

subprocess.Popen offers a wide range of options and flexibility for working with external processes. You can redirect input and output, set environment variables, and manage various other aspects of the child process. It’s a powerful tool for various tasks like running command-line tools, handling long-running processes, or even managing pipelines of commands.

Subprocess Popen Get Output

To get the output of a command executed using subprocess.Popen, you can use the subprocess.Popen.communicate() method. This method communicates with the process and returns the standard output and standard error streams. Here’s how you can do it:

import subprocess

# Define the command you want to run as a list of arguments
cmd = ["ls", "-l"]

# Use subprocess.Popen to start the process
process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)

# Communicate with the process and get its output and errors
output, errors = process.communicate()

# Print the output and errors (if any)
print("Output:", output)
print("Errors:", errors)

# Get the return code of the process (0 usually means success)
return_code = process.returncode
print("Return Code:", return_code)
Code language: Python (python)

In this example, process.communicate() is used to capture the standard output and standard error of the command. The stdout=subprocess.PIPE argument tells Popen to redirect the standard output of the command to a pipe, which can be accessed using process.communicate().

After calling process.communicate(), the output variable will contain the standard output of the command, and the errors variable will contain the standard error (if any). You can then process or print these outputs as needed.

Keep in mind that process.communicate() also waits for the process to complete. If you want to capture the output in real-time while the process is running, you can use other methods like process.stdout.readline() in a loop.

Python Subprocess Popen Return Code

subprocess.Popen, you can retrieve the return code of a subprocess using the returncode attribute of the Popen object. The returncode attribute stores the exit status of the subprocess, which is typically a numeric value indicating whether the subprocess completed successfully (usually 0 for success) or encountered an error (non-zero value).

Here’s how you can access the return code using returncode:

import subprocess

# Define the command you want to run as a list of arguments
cmd = ["ls", "-l"]

# Use subprocess.Popen to start the process
process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)

# Wait for the process to complete
return_code = process.wait()

# Get the return code of the process
print("Return Code:", return_code)
Code language: Python (python)

In this example, we use process.wait() to wait for the subprocess to complete and retrieve its return code. You can access the returncode attribute before or after waiting for the process, and it will provide you with the exit status of the subprocess.

The value of return_code will be 0 if the subprocess completed successfully. If there was an error, it will be a non-zero value indicating the type of error encountered. You can check the return_code to determine whether the subprocess succeeded or not and take appropriate actions based on it.

Read More;

• Python Subprocess Tutorial
• Subprocess Python Stdout
• Python Subprocess Stderr
• Python Asyncio Subprocess [Asynchronous Subprocesses]
• Subprocess.popen And Subprocess.run
• Python Subprocess Run In Background
• Python Execute Shell Command And Get Output
• Face Recognition Based Attendance System Using Python
• Python Subprocess Pipe With Example
• Python Subprocess Interactive
• Python Subprocess AWK
• What is subprocess.wait() With Example