New submission from Yclept Nemo: From: https://docs.python.org/dev/library/subprocess.html#popen-constructor "..., an existing file descriptor (a positive integer), an existing file object, and None." It should be made clear that the file object must be backed by an operating system file, i.e. must have a valid file descriptor. As it stands, the documentation suggests implicit concurrency: that any file object can be used, and on read/write from the subprocess/OS arbitrary python code will be executed, i.e. the python interpreter is pre-empted or python spawns a hidden I/O thread. Anyway, I'm pretty sure subprocess.Popen() just redirects the forked process' stdout/stdin/stderr to the file descriptors from the provided file object. ---------- assignee: docs@python components: Documentation messages: 264579 nosy: Yclept.Nemo, docs@python priority: normal severity: normal status: open title: Clarify Popen stdin, stdout, stderr versions: Python 3.6 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue26897> _______________________________________