subprocess(python3.7)

subprocess 主要是为了替换一下的模块函数,允许你执行一些命令,并获取返回的状态码和 输入,输出和错误信息。

os.system
os.spawn*

 

subprocess 有好多方法,本文主要在总结下之间的区别是什么,最后官方推荐使用哪个。

subprocess的主要方法:

subprocess.run(),subprocess.Popen(),subprocess.call   #这些模块都是基于Popen的

Python 3.5 之前

subprocess.call   //call 系列 都是等待命令执行完, Wait for command to complete

subprocess.call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None)

只返回执行结果的code  等同于subprocess.run(args).returncode

Note Do not use stdout=PIPE or stderr=PIPE with this function. The child process will block if it generates enough output to a pipe to fill up the OS pipe buffer as the pipes are not being read from.

############例子###
ret=subprocess.call(['ls', '-l'])     # ret 程序执行结果返回值,正确执行都是0


----------------------------捕获输出结果到一个文件里Redirecting STDOUT to a File---

with open('joe.txt', 'w') as f:    # 执行后joe.txt 文件内容为 Wed May 15 17:07:59 CST 2019
    subprocess.call(['date'], stdout=f)
    


-------捕获输出结果到字符串,Redirecting STDOUT to strings---

ret=subprocess.check_output()        #ret 为output内容(命令输出的内容) 等同于run(..., check=True, stdout=PIPE).stdout


-------------------
subprocess.check_call()   #和 subprocess.call 一样,只是返回值不是0就引起异常,raise CalledProcessError ,等同于 subprocess.run(…, check=True)



-----输入stdin ----------

with open('joe.txt', 'r') as fr
    subprocess.call(['cat'], stdin=f)
    
-------


######################################################
subprocess.Popen()   #最基本的subprocess模块

class subprocess.Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=True, shell=False, cwd=None, env=None, universal_newlines=None, startupinfo=None, creationflags=0, restore_signals=True, start_new_session=False, pass_fds=(), *, encoding=None, errors=None, text=None)

p = subprocess.Popen(['ls', '-l']) #返回的p是Popen 对象
p(Popen对象) 有一下方法
p.poll() 检查子进程(cmd) 是否结束  ,如果没有结束会返回None,结束就返回return returncode
p.returncode 程序之后后的返回码,一般正常结束会返回0,否则会返回其他值
p.wait()  等待子进程结束,然后返回returncode值

If the process does not terminate after timeout seconds, raise a TimeoutExpired exception. It is safe to catch this exception and retry the wait.

Note This will deadlock when using stdout=PIPE or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use Popen.communicate() when using pipes to avoid that.
Note The function is implemented using a busy loop (non-blocking call and short sleeps). Use the asyncio module for an asynchronous wait: see asyncio.create_subprocess_exec.


p.communicate() 和子进程交互,返回一个元祖,returns a tuple (stdout_data, stderr_data)
p.terminate() 终止子进程,相当于发送SIGTERM 信号,相当于kill (后面不加参数)
 p.kill() 终止子进程,相当于发送SIGKILL 信号,相当于kill -9 
p.stdin,p.stdout,p.stderr 分别是输入,输出,错误输出,在python3中都是byte类型需要decode转化 
p.returncode() 程序的返回状态 ,程序没有结束的话会返回None 
p.pid 返回程序的 pid
 p.send_signal(signal) 发送一个信号给子进程 
subprocess.Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=True, shell=False, cwd=None, env=None, universal_newlines=None, startupinfo=None, creationflags=0, restore_signals=True, start_new_session=False, pass_fds=(), *, encoding=None, errors=None, text=None)

 Popen 参数: 
------
 args, a sequence of program arguments or else a single string(参数是一个序列如,列表,元祖等。或者参数是一个字符串),默认情况下,如果args是序列,则要执行的程序是args中的第一项。如果args是一个字符串,需要设置shell=True,即开启一个shell 执行一个字符串的命令,或者序列的第一项 
-----
 bufsize 参数,stdin,stdout,stderr的缓存参数
 executable 参数 
@@@@@@@@@@@@@@@@@@@@@@@@@@@@ ,shell=True时 executable=, 用于替换系统默认的shell(一般是bash),
 p = subprocess.Popen('echo $0',shell=True,stdout=subprocess.PIPE,stderr=subprocess.PIPE,executable='/bin/zsh') out,_=p.communicate() print(out.decode()) 
输出>>>/bin/zsh 
@@@@@@@@@@@@@@@@@@@@@@@@@ shell=False时 executable=xxx,xxx会替换序列的第一项,一下'ls' 替换了'cat' 最终执行了 ls 'a.py','a.txt','b.txt'
 p = subprocess.Popen(['cat','a.py','a.txt','b.txt'],stdout=subprocess.PIPE,stderr=subprocess.PIPE,executable='ls') out,_=p.communicate() print(out.decode()) 
输出>>>a.py a.txt b.txt

 -----

stdin=None, stdout=None, stderr=None 和输入,输出,错误输出有关,

想要捕捉这些信息可以设置为 将值设置为subprocess.PIPE,stdin=subprocess.PIPE,stdout=subprocess.PIPE,stderr=subprocess.PIPE 如果想要达到2>&1 可以设置为stdout=subprocess.PIPE,stderr=subprocess.STDOUT 这些内容 stdin 如输入("haha") 可以通过p.stdin.write(b"hahha");p.stdin.close() 或者 out,_=p.communicate(b'haha') stdout,stderr 可以通过p.stdout.readline(),p.stderr.readline() [就是文件描述符的一些参数如read(),readline等]

 

------

 

close_fds=True 子进程是否继承文件描述符,如果false 将关闭除了0,1,2之外的所有文件描述符。 print( p.stdin.fileno()) #查看自身对应的(stdin/stdout)的文件描述符 参考一下遇到的问题close_fds(python2.x遇到的问题???!!!) https://stackoverflow.com/questions/19950185/python-close-fds-not-clear http://drmingdrmer.github.io/tech/programming/2017/11/20/python-concurrent-popen.html

-------

shell=True 是否在shell中执行,参考args 说明

--------

cwd 当前的工作目录,如果有值,就会进入cd 到这个目录执行args命令

-----

text=True,和universal_newlines=True一样,universal_newlines只是为了向后兼容 都是让stdxxx以文本模式输出,而不是默认的二进制模式

If encoding or errors are specified, or text is true, the file objects stdin, stdout and stderr are opened in text mode with the specified encoding and errors, as described above in Frequently Used Arguments. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode.

-----

 

python3.5 以后官方推荐使用run

p=subprocess.run(args, ***, stdin=None, input=None, stdout=None, stderr=None, capture_output=False, shell=False, cwd=None, timeout=None, check=False, encoding=None, errors=None, text=None, env=None, universal_newlines=None)

 run 也是需要等进程结束后才返回结果,所以没有结束p.stdout等就不会输出结果

 

run的参数,和Popen 一样

capture_outputstdout=PIPEstderr=PIPE

timeout 设置子进程超时时间,超时引起 TimeoutExpired异常

The timeoutPopen.communicate(). If the timeout expires, the child process will be killed and waited for. The TimeoutExpired exception will be re-raised after the child process has terminated

 

input=xxx 相当于 Popen.communicate(xxx)和自动创建 stdin=PIPE

The inputPopen.communicate()encodingerrorstextPopenstdin=PIPE, and the stdin argument may not be used as well.

check check=True 如果程序返回状态码不是0 就引起异常CalledProcessError

If checkCalledProcessErrorexception will be raised. Attributes of that exception hold the arguments, the exit code, and stdout and stderr if they were captured.

p=subprocess.run(), 执行run后会返回 CompletedProcess类型 实例 P

实例P 有如下方法

p.args

p.returncode

p.stdout

p.stderr

p.check_returncode

 

Python Process 结果 python3 process_子进程