Python - Execute Process -> Block till it exits & Suppress Output
I'm using the following to execute a process and hide its output from Python. It's in a loop though, and I need a way to block until the sub process has terminated before moving to the next iteration.
subprocess.开发者_如何学编程Popen(["scanx", "--udp", host], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
Use subprocess.call()
. From the docs:
subprocess.call(*popenargs, **kwargs)
Run command with arguments. Wait for command to complete, then return the returncode attribute. The arguments are the same as for the Popen constructor.
Edit:
subprocess.call()
uses wait()
, and wait()
is vulnerable to deadlocks (as Tommy Herbert pointed out). From the docs:
Warning: This will deadlock if the child process generates enough output to a stdout or stderr pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use communicate() to avoid that.
So if your command generates a lot of output, use communicate()
instead:
p = subprocess.Popen(
["scanx", "--udp", host],
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
out, err = p.communicate()
If you don't need output at all you can pass devnull to stdout
and stderr
. I don't know if this can make a difference but pass a bufsize. Using devnull now subprocess.call
doesn't suffer of deadlock anymore
import os
import subprocess
null = open(os.devnull, 'w')
subprocess.call(['ls', '-lR'], bufsize=4096, stdout=null, stderr=null)
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