为什么子进程不以 Python 2.7 终止？

Question

我有一个代码生成一个进程 subprocess.Popen:

from subprocess import check_call, CalledProcessError, Popen, PIPE
cmd="while true; do echo 123; done | grep -m1 123"
proc = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE)
out, err = proc.communicate()

当我用 Python 3.9.2 运行时，它会按预期立即终止。但是，当我运行它与 Python 2.7 挂起时。似乎 Python 2.7 等待 shell 无限循环终止，但它永远不会终止。我也可以让这段代码在 Python 2.7 下终止吗？

Answer 1

找到相关问题 Python subprocess.Popen blocks with shell and pipe for Python 2.7. The problem is that in Python 2.7 SIGPIPE signal is ignored by default and therefore while true loop ignores the fact that grep terminates on first match. There is unresolved Python issue for this https://bugs.python.org/issue1652。在 Python 3 上，subprocess.Popen 有一个额外的参数 restore_signals=True，因此上面的代码按原样工作。对于 Python 2.7，可以这样修改以恢复 SIGPIPE 信号：

from subprocess import check_call, CalledProcessError, Popen, PIPE
import signal

def restore_signals():
    signals = ('SIGPIPE', 'SIGXFZ', 'SIGXFSZ')
    for sig in signals:
        if hasattr(signal, sig):
            signal.signal(getattr(signal, sig), signal.SIG_DFL)

cmd="while true; do echo 123; done | grep -m1 123"
proc = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE, preexec_fn=restore_signals)
out, err = proc.communicate()

为什么子进程不以 Python 2.7 终止？

Why subprocess does not terminate with Python 2.7 only?

python

python-2.7

python-3.x