Python Learning ———— Module subprocess

subprocess Module

The subprocess module targets to start a new process and communicate with it.

1. Call: Executes the program, waits for it to complete, returns the status code.

Importsubprocess
Ret1 = Subprocess.call (["CP","-P"],Shell=True)
Ret2 = Subprocess.call (["CP","-P"],Shell=False)

Shell = True allows the shell to be a string form.

def Call (*popenargs, **kwargs):
return Popen (*popenargs, **kwargs). Wait ()

2, Call_check () calls the preceding call () function, and throws an exception if the return value is nonzero.

defCheck_call (*popenargs, **kwargs):
Retcode = Call (*popenargs, **kwargs)
ifRetcode:
cmd = Kwargs.get ("args")
offcmd isNone:
cmd = popenargs[0]
RaiseCalledprocesserror (Retcode, cmd)
return0

3, Check_output (): Executes the program, if the return code is 0, returns the execution result.

defcheck_output (*popenargs, **kwargs):
if' stdout 'inchKwargs:
RaiseValueError(' stdout argument not allowed, it'll be overridden. ')
Process = Popen (stdout=pipe, *popenargs, **kwargs)
Output, Unused_err = Process.communicate ()
Retcode = Process.poll ()
ifRetcode
cmd = Kwargs.get ("args")
ifcmd isNone:
cmd = popenargs[0]
Raisecalledprocesserror (retcode, CMD,Output=Output)
returnOutput

4. Subprocess also provides a very important class Popen: Execute complex system commands.

classPopen (Object):
def__init__( Self, args, bufsize=0, executable=None,
stdin=None, stdout=None, stderr=None,
preexec_fn=None, close_fds=False, Shell=False,
Cwd=None, env=None, universal_newlines=False,
startupinfo=None, creationflags=0):

Args	The shell command can be a string or a list
BufSize	0 unbuffered, 1 row buffer, other buffer size, negative system buffering
Executable	Generally not
stdin stdout stderr	Standard output, output, error handle
Preexec_fn	Executes only on UNIX platforms, specifying an executable object that is called before the child process executes
Close_fds	under the Windows platform, if Close_fds is set to true, the newly created child process will not inherit the input, output, and error pipes of the parent process. Therefore, you cannot set Close_fds to true while redirecting the standard input, output, and error (stdin, stdout, stderr) of the child process.
Shell	Ditto
Cwd	Used to set the current directory of the child process
Env	Environment variables for setting child processes
Universal_newlines	Various newline characters are set to \ n
Startupinfo	struct passed to CreateProcess under window, only valid under Windows
Creationflags	Under Windows, passing Create_new_console creates its own console window, which is valid under Windows

Methods of Popen:

Poll ()	Check if end, set return value
Wait ()	Wait for end, set return value
Communicate ()	parameter is standard input, return standard output and error
Send_signal ()	Send a signal, mainly used under Linux
Terminate ()	Terminating signal
Kill ()	Kill process
Pid	Process ID
ReturnCode	Process return value
stdin stdout stderr	parameter, it is useful to specify pipe in the

Example:

Import subprocessobj = subprocess. Popen (["Python"], stdin=subprocess. PIPE, Stdout=subprocess. PIPE, Stderr=subprocess. PIPE) Obj.stdin.write (' Print 1 \ n ') obj.stdin.write (' Print 2 \ n ') obj.stdin.write (' Print 3 \ n ') obj.stdin.write (' Print 4 \ n ') obj.stdin.close () Cmd_out = Obj.stdout.read () obj.stdout.close () Cmd_error = Obj.stderr.read () obj.stderr.close () Print Cmd_outprint Cmd_error

Reference URL: http://www.cnblogs.com/wupeiqi/articles/4963027.html

Python Learning ———— Module subprocess