th 339 - Subprocess.Popen vs Subprocess.Run: Understanding the Differences.

Subprocess.Popen vs Subprocess.Run: Understanding the Differences.

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th?q=What Is The Difference Between Subprocess.Popen And Subprocess - Subprocess.Popen vs Subprocess.Run: Understanding the Differences.

If you are into Python programming, you must have come across the subprocess module, particularly two of its popular variants, subprocess.Popen and Both these methods are generally used to execute external commands and shell scripts in Python programs. However, there are certain differences between the two that developers must be aware of. This article aims to throw some light on those differences and help you understand which one to use when.

Subprocess.Popen and may look similar but have subtle differences that make them distinct from each other. The major difference is that subprocess.Popen returns a Popen object, while doesn’t. Subprocess.Popen creates a new process and runs an external command or script, and keeps the input/output streams for that process available if required. Meanwhile, runs the command and waits for it to complete before it returns control to the parent process.

Choosing the right method while writing your Python code is crucial. While subprocess.Popen offers more control and flexibility, it may be an overkill for simple command-line execution. On the other hand, can be simpler but may not work in cases where more advanced features like reading from and writing to input/output streams are needed. In conclusion, understanding the differences between subprocess.Popen and will help you write efficient code that fulfills your specific requirements.

In a world where software development is evolving every day, it’s necessary to keep up-to-date with the tools we use. Knowing when to use subprocess.Popen and when to use can save time, reduce errors and even spark creativity. Take some time to research and experiment with both these methods, and choose the one which suits your needs and goals. So, what are you waiting for? Dive into the world of subprocess.Popen and today!

th?q=What%20Is%20The%20Difference%20Between%20Subprocess.Popen%20And%20Subprocess - Subprocess.Popen vs Subprocess.Run: Understanding the Differences.
“What Is The Difference Between Subprocess.Popen And Subprocess.Run” ~ bbaz


Subprocess module is an essential part of the Python programming language, which allows running processes and interacting with their input/output errors & return codes. There are two significantly used functions in the Subprocess module which include Popen and Run, which execute a child program in a new process.

What is Subprocess?

The Subprocess module is a built-in feature in Python that provides rich capabilities for spawning new processes from the main process. It interacts with the child process in various forms, such as pipes for input/output/error streams, or wait for completion and retrieve success and return code. The module aims to offer convenience, security, and compatibility to manage multiple activities or programs efficiently.

How does Popen Function work?

The Popen function starts a new child process by accepting the command as a parameter in the form of a list, string, or any argument as accepted by the shell. It returns a Popen object representing the spawned process, and its methods allow interaction and control over the child process, such as passing input to its STDIN, retrieving output/error from its STDOUT/STDERR, or waiting for its completion, etc.

How does Run Function Work?

The Run function is a relatively recent addition in Python 3.5 that also executes a child program as provided in the same format and parameters as Popen. However, it runs synchronously, waits for the process to complete, and captures its output and error values in the CompletedProcess object, unlike Popen where these need to be retrieved explicitly.

Comparison Table

Features Popen Run
Asynchronous Yes No
Output/Error Capture Explicit Implicit
Return Value Popen Object CompletedProcess Object

Key Differences between Subprocess.Popen and Subprocess.Run

Asynchronous Execution

The most significant difference between Popen and Run is that Popen function executes the command asynchronously, whereas Run function performs synchronous execution. Asynchronous execution means the child process runs parallelly to the parent process, and the parent process doesn’t wait for the completion of the child. In comparison, synchronous execution means the calling process waits for the child process to complete its execution.

Output/Error Capture

The second significant difference between Popen and Run is their respective output/error capturing capabilities. Since Popen runs asynchronously, it doesn’t automatically capture the output or error values produced by the child process. Instead, the process’s standard output, standard error, or any other streams must be explicitly retrieved or passed as a parameter during its initialization, which can then be used later for further processing or handling. In contrast, Run inherently captures output and errors, which can be later accessed using the CompletedProcess object.

Return Value

The final difference between Popen and Run functions is their respective return values. As mentioned earlier, Popen returns a Popen object representing the child process while Run returns a CompletedProcess object containing the output, error, and return code, among other process details. This difference means that Run is more focused on providing the final result, while Popen aims to give more control over the execution and handling of child processes.


In conclusion, Subprocess module’s Popen and Run functions are powerful tools for managing and interacting with child processes in Python. However, their differences in asynchronous/synchronous execution, output/error capture, and return values make them better suited for different usage scenarios. Therefore, it is recommended to choose between Popen or Run solely based on the requirements and objectives of the program rather than general familiarity or convenience.

Thank you for taking the time to read and learn about the differences between Subprocess.Popen and Subprocess.Run. Understanding these differences can greatly improve your coding efficiency and ensure that your programs are running optimally.

Whether you’re new to Python or have been using it for years, it’s important to stay knowledgeable about its various libraries and functions. By understanding when to use Popen and when to use Run, you can better customize your code to fit your specific needs and goals.

So next time you’re working on a project that involves subprocesses, remember the differences between Popen and Run and choose the one that’s best suited for your task at hand. And as always, keep learning and exploring new ways to enhance your Python skills!

People often have questions about the differences between Subprocess.Popen and Subprocess.Run. Here are some common ones:

  1. What is Subprocess.Popen?
  • Subprocess.Popen is a method in the subprocess module that allows you to spawn a new process and communicate with it through pipes.
  • What is Subprocess.Run?
    • Subprocess.Run is a newer method in the subprocess module that provides a simpler and more efficient way to run a command and capture its output.
  • What are the key differences between Subprocess.Popen and Subprocess.Run?
    • Subprocess.Popen gives you more control over the process and its input/output streams, but requires more code to set up.
    • Subprocess.Run is easier to use and can be more efficient, but is less flexible in terms of input/output handling.
  • When should I use Subprocess.Popen?
    • You should use Subprocess.Popen when you need fine-grained control over the process and its input/output streams.
    • For example, if you need to interact with the process in real-time, or if you need to handle complex input/output scenarios.
  • When should I use Subprocess.Run?
    • You should use Subprocess.Run when you need a simple and efficient way to run a command and capture its output.
    • For example, if you just need to run a command and get its output as a string, or if you need to run a command as a background task.