子流程引发CalledProcessError异常时检查命令的返回码

Question

我想stdout在python（3）脚本中捕获shell命令的流，并能够同时检查shell命令的返回代码（如果它返回错误）（即，如果它的返回代码是不为0）。

subprocess.check_output似乎是执行此操作的适当方法。从subprocess的手册页：

check_output(*popenargs, **kwargs)
    Run command with arguments and return its output as a byte string.

    If the exit code was non-zero it raises a CalledProcessError.  The
    CalledProcessError object will have the return code in the returncode
    attribute and output in the output attribute.

尽管如此，当失败时，我仍然无法从shell命令获取返回代码。我的代码如下所示：

import subprocess
failing_command=['ls', 'non_existent_dir']

try:
    subprocess.check_output(failing_command)
except:
    ret = subprocess.CalledProcessError.returncode  # <- this seems to be wrong
    if ret in (1, 2):
        print("the command failed")
    elif ret in (3, 4, 5):
        print("the command failed very much")

这段代码在处理异常本身时引发了一个异常：

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
AttributeError: type object 'CalledProcessError' has no attribute 'returncode'

我承认我不知道我哪里错了。

Answer 1

要同时获取过程输出和返回的代码：

from subprocess import Popen, PIPE

p = Popen(["ls", "non existent"], stdout=PIPE)
output = p.communicate()[0]
print(p.returncode)

subprocess.CalledProcessError是一类。要访问，请returncode使用异常实例：

from subprocess import CalledProcessError, check_output

try:
    output = check_output(["ls", "non existent"])
    returncode = 0
except CalledProcessError as e:
    output = e.output
    returncode = e.returncode

print(returncode)