Popen stdout/stderr generator by means of select.select

execution.py

import shlex
import subprocess
import select


class stdout(str):

    """A string representation from stdout."""


class stderr(str):

    """A string representation from stderr."""


class Execution(object):

    """Provides an iterator over stdout and stderr lines from Popen process."""

    def __init__(self, command):
        if isinstance(command, subprocess.Popen):
            self.proc = command

        else:
            self.proc = subprocess.Popen(
                isinstance(command, basestring) and shlex.split(command) or command,
                shell=False,
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE,
                # stdin=subprocess.PIPE,
            )

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        pass

    def __iter__(self):
        proc = self.proc

        stdout_fd = proc.stdout.fileno()
        stderr_fd = proc.stderr.fileno()

        line_factory = {
            stdout_fd: lambda: stdout(proc.stdout.readline()),
            stderr_fd: lambda: stderr(proc.stderr.readline())
        }

        reads = [stdout_fd, stderr_fd]

        while True:
            rx, _, _ = select.select(reads, [], [])

            for fd in rx:
                factory = line_factory[fd]

                while True:
                    line = factory()

                    if line == '':
                        break

                    yield line

            if proc.poll() is not None:
                break

    @property
    def exitcode(self):
        return self.proc.returncode

    @property
    def pid(self):
        return self.proc.pid


def test_execution():
    with Execution('ls -la') as exe:
        for line in exe:
            print line.__class__.__name__, line,

    print "Exited with:", exe.exitcode