[Python编程(第4版)].(Programming.Python.4th.Edition).Mark.Lutz.文字版

>>> pipe.wait()

42

>>> call('python testexit_sys.py')

Bye sys world

42

>>> pipe = Popen('python testexit_sys.py', stdout=PIPE)

>>> pipe.communicate()

(b'Bye sys world\r\n', None)

>>> pipe.returncode

42

The subprocess module works the same on Unix-like platforms like Cygwin, but unlike
os.popen, the exit status is not encoded, and so it matches the Windows result (note
that shell=True is needed to run this as is on Cygwin and Unix-like platforms, as we
learned in Chapter 2; on Windows this argument is required only to run commands
built into the shell, like dir):

[C:\...\PP4E\System\Exits]$ python

>>> from subprocess import Popen, PIPE, call

>>> pipe = Popen('python testexit_sys.py', stdout=PIPE, shell=True)

>>> pipe.stdout.read()

b'Bye sys world\n'

>>> pipe.wait()

42

>>> call('python testexit_sys.py', shell=True)

Bye sys world

42

Process Exit Status and Shared State

Now, to learn how to obtain the exit status from forked processes, let’s write a simple
forking program: the script in Example 5-17 forks child processes and prints child
process exit statuses returned by os.wait calls in the parent until a “q” is typed at the
console.

Example 5-17. PP4E\System\Exits\testexit_fork.py

"""
fork child processes to watch exit status with os.wait; fork works on Unix
and Cygwin but not standard Windows Python 3.1; note: spawned threads share
globals, but each forked process has its own copy of them (forks share file
descriptors)--exitstat is always the same here but will vary if for threads;
"""

import os
exitstat = 0

def child(): # could os.exit a script here
global exitstat # change this process's global
exitstat += 1 # exit status to parent's wait

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