我正在编写一个管道，该管道以特定顺序使用一堆bash调用。
如何确定我的命令是否抛出错误？
例如，我正在运行带有子进程的Java程序，当该进程出错时，它不会警告我或退出。
subprocess或我的process对象中是否有使用此实用程序的东西？
process = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
process.wait()
当我尝试来自Python: "subprocess.Popen" check for success and errors的建议时，出现以下错误：
In [6]: subprocess.check_call(process)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-6-f8f8752a245f> in <module>
----> 1 subprocess.check_call(process)
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in check_call(*popenargs, **kwargs)
284 check_call(["ls", "-l"])
285 """
--> 286 retcode = call(*popenargs, **kwargs)
287 if retcode:
288 cmd = kwargs.get("args")
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in call(timeout, *popenargs, **kwargs)
265 retcode = call(["ls", "-l"])
266 """
--> 267 with Popen(*popenargs, **kwargs) as p:
268 try:
269 return p.wait(timeout=timeout)
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags, restore_signals, start_new_session, pass_fds, encoding, errors)
707 c2pread, c2pwrite,
708 errread, errwrite,
--> 709 restore_signals, start_new_session)
710 except:
711 # Cleanup if the child failed starting.
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in _execute_child(self, args, executable, preexec_fn, close_fds, pass_fds, cwd, env, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite, restore_signals, start_new_session)
1218 args = [args]
1219 else:
-> 1220 args = list(args)
1221
1222 if shell:
TypeError: 'Popen' object is not iterable
In [7]: subprocess.check_output(process)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-7-0ec9e7eac1c2> in <module>
----> 1 subprocess.check_output(process)
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in check_output(timeout, *popenargs, **kwargs)
334
335 return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
--> 336 **kwargs).stdout
337
338
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in run(input, timeout, check, *popenargs, **kwargs)
401 kwargs['stdin'] = PIPE
402
--> 403 with Popen(*popenargs, **kwargs) as process:
404 try:
405 stdout, stderr = process.communicate(input, timeout=timeout)
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags, restore_signals, start_new_session, pass_fds, encoding, errors)
707 c2pread, c2pwrite,
708 errread, errwrite,
--> 709 restore_signals, start_new_session)
710 except:
711 # Cleanup if the child failed starting.
~/anaconda/envs/µ_env/lib/python3.6/subprocess.py in _execute_child(self, args, executable, preexec_fn, close_fds, pass_fds, cwd, env, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite, restore_signals, start_new_session)
1218 args = [args]
1219 else:
-> 1220 args = list(args)
1221
1222 if shell:
TypeError: 'Popen' object is not iterable
答案 0 :(得分：1)
check_call和check_output都应传递命令系统要运行的命令列表（与发送到Popen的命令列表相同）。这两个都阻止了调用，这意味着Python将等到它们完成运行更多代码之后。
使用Popen将命令列表发送到命令系统，但不阻止进一步执行Python代码。您可以使用.poll对象的Popen方法来检查过程，也可以使用.communicate进行阻塞调用，这将返回标准输出和标准错误流的元组。
假设您想要执行的命令的结果，并且该命令将向错误流正确报告错误，则可以使用：
process = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = process.communicate()
if err:
print('The process raised an error:', err.decode())
Popen：import subprocess
# first a command that works correctly
proc = subprocess.Popen(['ls', '-a'], , stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = proc.communicate()
if not err:
print('--No errors--\n', out.decode())
else:
print('--Error--\n', err.decode())
# prints:
--No errors--
anaconda3
Desktop
Documents
Downloads
# next a command generates and error, the `-w` switch is invalid
proc = subprocess.Popen(['ls', '-w'], , stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = proc.communicate()
if not err:
print('--No errors--\n', out.decode())
else:
print('--Error--\n', err.decode())
# prints:
--Error--
ls: option requires an argument -- 'w'
Try 'ls --help' for more information.
check_call check_call将引发Python异常，如果命令系统的返回代码不为0。
# first with a working command:
ret_code = subprocess.check_call(['ls', '-a'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
ret_code
# returns:
0
# and now with the command that generates an error:
ret_code = subprocess.check_call(['ls', '-w'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
# raises an exception:
---------------------------------------------------------------------------
CalledProcessError Traceback (most recent call last)
<ipython-input-25-3cd5107991a2> in <module>()
----> 1 ret_code = subprocess.check_call(['ls', '-w'], stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
~/anaconda3/lib/python3.6/subprocess.py in check_call(*popenargs, **kwargs)
289 if cmd is None:
290 cmd = popenargs[0]
--> 291 raise CalledProcessError(retcode, cmd)
292 return 0
293
CalledProcessError: Command '['ls', '-w']' returned non-zero exit status 2.
要处理该异常，请使用try/except块。
try:
ret_code = subprocess.check_call(['ls', '-w'], stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
except subprocess.CalledProcessError as e:
ret_code = e.returncode
print('An error occurred. Error code:', ret_code)
# prints:
An error occurred. Error code: 2
check_output check_output与check_call非常相似，如果命令系统的返回代码不为0，它将引发Python异常。但是，如果返回代码为0，则它将返回在标准输出流中输出。
# just with the error process this time
try:
ret_code = subprocess.check_output(['ls', '-w'], stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
except subprocess.CalledProcessError as e:
ret_code = e.returncode
print('An error occurred. Error code:', ret_code)
# prints:
An error occurred. Error code: 2