[issue23750] Clarify difference between os.system/subprocess.call in section "Replacing os.system()"
New submission from Andreas Sommer: Reading over the section "Replacing os.system()" (https://docs.python.org/2/library/subprocess.html#replacing-os-system), one might assume that the return value of os.system and subprocess.call are equivalent. status = os.system("mycmd" + " myarg") # becomes status = subprocess.call("mycmd" + " myarg", shell=True) However, they are not. Example: import sys import os import subprocess print subprocess.call("false") print os.system("false") gives 1 and 256, respectively. Maybe this could be rephrased for clarity, or a hint added. ---------- assignee: docs@python components: Documentation messages: 239028 nosy: Andreas Sommer, docs@python priority: normal severity: normal status: open title: Clarify difference between os.system/subprocess.call in section "Replacing os.system()" type: enhancement _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23750> _______________________________________
Martin Panter added the comment: Another difference is that (at least POSIX) system() blocks SIGINT and SIGQUIT while the child is running. Compare: $ python3 -c 'print("Waiting"); import os; print("Returned", os.system("sleep 3 && exit 3"))' Sleeping Returned 768 $ python3 -c 'print("Sleeping"); import os; print("Returned", os.system("sleep 3 && exit 3"))' Waiting ^CReturned 2 # Hit Ctrl+C during sleep command $ python3 -c 'print("Sleeping"); import subprocess; print("Returned", subprocess.call("sleep 3 && exit 3", shell=True))' Sleeping Returned 3 $ python3 -c 'print("Sleeping"); import subprocess; print("Returned", subprocess.call("sleep 3 && exit 3", shell=True))' Sleeping ^CTraceback (most recent call last): File "<string>", line 1, in <module> File "/usr/lib/python3.4/subprocess.py", line 539, in call return p.wait(timeout=timeout) File "/usr/lib/python3.4/subprocess.py", line 1566, in wait (pid, sts) = self._try_wait(0) File "/usr/lib/python3.4/subprocess.py", line 1514, in _try_wait (pid, sts) = _eintr_retry_call(os.waitpid, self.pid, wait_flags) File "/usr/lib/python3.4/subprocess.py", line 491, in _eintr_retry_call return func(*args) KeyboardInterrupt [Exit 1] ---------- nosy: +vadmium _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23750> _______________________________________
Martin Panter added the comment: Here is a patch: * Use different return value variable names and point out that they are encoded differently * Add another bullet point about signal handling * Fix os.system() documentation of the return value. My understanding is it is the C standard that does not define the return value, and Posix essentially means Unix. ---------- keywords: +patch stage: -> patch review versions: +Python 2.7, Python 3.4, Python 3.5, Python 3.6 Added file: http://bugs.python.org/file39767/system-subprocess.patch _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23750> _______________________________________
Irit Katriel <iritkatriel@yahoo.com> added the comment: The patch needs to be converted to a github PR. ---------- keywords: +easy nosy: +iritkatriel title: Clarify difference between os.system/subprocess.call in section "Replacing os.system()" -> doc: Clarify difference between os.system/subprocess.call in section "Replacing os.system()" versions: +Python 3.10, Python 3.11, Python 3.9 -Python 2.7, Python 3.4, Python 3.5, Python 3.6 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23750> _______________________________________
participants (3)
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Andreas Sommer -
Irit Katriel
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Martin Panter