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subprocess-popen-preexec-fn (PLW1509)#

Derived from the Pylint linter.

What it does#

Checks for uses of subprocess.Popen with a preexec_fn argument.

Why is this bad?#

The preexec_fn argument is unsafe within threads as it can lead to deadlocks. Furthermore, preexec_fn is targeted for deprecation.

Instead, consider using task-specific arguments such as env, start_new_session, and process_group. These are not prone to deadlocks and are more explicit.


import os, subprocess

subprocess.Popen(foo, preexec_fn=os.setsid)
subprocess.Popen(bar, preexec_fn=os.setpgid(0, 0))

Use instead:

import subprocess

subprocess.Popen(foo, start_new_session=True)
subprocess.Popen(bar, process_group=0)  # Introduced in Python 3.11