[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
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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
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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