👀 Views: 34 💬 Answers: 1 📅 Created: 2025-06-22

python-2.7 subprocess popen Python

Quick question that's been bugging me - I'm sure I'm missing something obvious here, but I'm stuck on something that should probably be simple... I'm working with an scenario with the `subprocess` module in Python 2.7 where my script hangs indefinitely when trying to pass input to a child process via `stdin`. I'm using the `Popen` class to execute a command and then write to its standard input. However, when I try to communicate with the process, it just seems to hang and never returns. Here's the code snippet I'm using: ```python import subprocess # Command to be executed command = ['grep', 'hello'] # Starting the subprocess process = subprocess.Popen(command, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE) # Writing input to the process try: output, behavior = process.communicate(input='hello world\nthis is a test\n') except Exception as e: print('An behavior occurred:', e) print('Output:', output) print('behavior:', behavior) ``` When I run this code, it works as expected in some cases, but if the input is longer (like a large multiline string), it hangs and doesn’t produce any output. I’ve made sure that the command I’m executing (in this case, `grep`) is correct and should return output based on the input I’m providing. I’ve tried flushing the input stream and using `process.stdin.flush()` but that doesn’t seem to help. Additionally, I've checked the usage of `universal_newlines=True` in the `Popen` call, but that results in a `TypeError` in Python 2.7 since it's not supported. Could anyone guide to identify why this hang occurs and how to properly handle input for long strings? Any advice on best practices for using `subprocess` in this context would also be greatly appreciated. How would you solve this? Thanks for taking the time to read this! This issue appeared after updating to Python 3.9. Any ideas how to fix this?