Python parallel operation-parent-child process Subprocess Library

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Reference links

Http://www.cnblogs.com/vamei/archive/2012/09/23/2698014.html

The concept of a parent-child process

A process can fork itself, become a child process, and let the child process to exec another program

Sub-processes in Python

In Python, with the subprocess package, fork a child process and run an external program

Points to think about

Whether the parent process blocks after the child process is created

What the function returns

ReturnCode not 0 o'clock (description is not a child process), how the parent process handles

Simple to use Subprocess.call ()

Parent process waits for child process to complete

Return exit information (ReturnCode)

Subprocess.check_call ()

Parent process waits for child process to complete

Returns 0

The exit information (ReturnCode) is checked and subprocess is thrown if ReturnCode is not 0. Calledprocesserror error, the object contains a ReturnCode property, available try...except ... To check

Subprocess.check_output ()

Parent process waits for child process to complete

Returns the output of the child process to the standard output

The exit information (ReturnCode) is checked and subprocess is thrown if ReturnCode is not 0. The Calledprocesserror error, which contains the ReturnCode property and the output property, outputs a standard output, and is also available try...except ... To check

Simple Use example list parameter

The program name ls and parameter-L are placed in a table passed to Subprocess.call ()

rc = Subprocess.call (["LS", "-l"])

String argument

Run a shell first, then use the shell to interpret the entire string

Some of the shell's built-in commands must be run using the shell

out = Subprocess.call ("Ls-l", Shell=true)

Advanced usage-Child process parallelism & text Flow subprocess. Popen class

__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)

After the Popen object is created, the parent process does not automatically wait for the child process to complete

Child = subprocess. Popen (["Ping", "-C", "5", "www.google.com"])

Child.pid-PID of child process

Child.stdin-stdin of child processes

Child.stdout-stdout of child processes

Child.stderr-stderr of child processes

Child.wait ()-Parent process waits for child process to complete

Child.poll ()-Check child process status

Child.send_signal (SIG)-sends a signal to a child process

Child.kill ()-Terminates child process

Child.terminate ()-Terminates the child process, equal to kill

Child.communicate (Input=none)-After giving the child process stdin, gets the output stream of the child process, returning the result to the tuple type (STDOUT,STDERR). Be aware that this method will block the current process.

Advanced use example Parent-child process parallelism

Child = subprocess. Popen (["Ping", "-C", "5", "www.google.com"])

Print ("Parent process")

Child process stdout directs another subprocess stdin

Child1 = subprocess. Popen (["LS", "-l"], stdout=subprocess. PIPE)

Child2 = subprocess. Popen (["WC"], stdin=child1.stdout,stdout=subprocess. PIPE)

out = Child2.communicate ()

The child process waits for the current process input

Child = subprocess. Popen (["Cat"], stdin=subprocess. PIPE)

Child.communicate ("Vamei")

Python parallel operation-parent-child process Subprocess Library