How to use the py.process.cmdexec function in py

def lsof_check():
    pid = os.getpid()
    try:
        out = py.process.cmdexec("lsof -p %d" % pid)
    except (py.process.cmdexec.Error, UnicodeDecodeError):
        # about UnicodeDecodeError, see note on pytester
        pytest.skip("could not run 'lsof'")
    yield
    out2 = py.process.cmdexec("lsof -p %d" % pid)
    len1 = len([x for x in out.split("\n") if "REG" in x])
    len2 = len([x for x in out2.split("\n") if "REG" in x])
    assert len2 < len1 + 3, out2

def matching_platform(self):
        try:
            py.process.cmdexec("lsof -v")
        except (py.process.cmdexec.Error, UnicodeDecodeError):
            # cmdexec may raise UnicodeDecodeError on Windows systems with
            # locale other than English:
            # https://bitbucket.org/pytest-dev/py/issues/66
            return False
        else:
            return True

def serve_bg(repopath):
    pidfile = py.path.local(repopath).join('pid')
    port = 10000
    e = None
    while port < 10010:
        cmd = 'svnserve -d -T --listen-port=%d --pid-file=%s -r %s' % (
               port, pidfile, repopath)
        print(cmd)
        try:
            py.process.cmdexec(cmd)
        except py.process.cmdexec.Error:
            e = sys.exc_info()[1]
        else:
            # XXX we assume here that the pid file gets written somewhere, I
            # guess this should be relatively safe... (I hope, at least?)
            counter = pid = 0
            while counter < 10:
                counter += 1
                try:
                    pid = pidfile.read()
                except py.error.ENOENT:
                    pass
                if pid:
                    break
                time.sleep(0.2)
            return port, int(pid)

def _exec_lsof(self):
        pid = os.getpid()
        return py.process.cmdexec("lsof -Ffn0 -p %d" % pid)

import sys
if sys.version_info > (3, 0):
    sys.stdin = sys.stdin.detach()
options = serializer.UnserializationOptions(%s)
loader = serializer.Unserializer(sys.stdin, options)
obj = loader.load()
sys.stdout.write(type(obj).__name__ + "\n")
sys.stdout.write(repr(obj))""" % (option_args,))
        popen = subprocess.Popen([str(self.executable), str(script_file)],
                                 stdin=subprocess.PIPE,
                                 stderr=subprocess.PIPE,
                                 stdout=subprocess.PIPE)
        stdout, stderr = popen.communicate(data.encode("latin-1"))
        ret = popen.returncode
        if ret:
            raise py.process.cmdexec.Error(ret, ret, str(self.executable),
                                           stdout, stderr)
        return [s.decode("ascii") for s in stdout.splitlines()]

def run_tests(path, envvars='', args=''):
    pytestpath = pypath.join('bin/py.test')
    cmd = ('PYTHONPATH="%s" %s python "%s" %s "%s"' %
            (pypath.dirpath(), envvars, pytestpath, args, path))
    print cmd
    py.process.cmdexec(cmd)

def _exec(self, cmd):
        python = self.python 
        old = self.location.chdir()
        try:
            cmd = "%(python)s setup.py %(cmd)s" % locals()
            log.command(cmd)
            out = py.process.cmdexec(cmd)
        finally:
            old.chdir()
        return out

""" return stdout text from executing a system child process,
            where the 'self' path points to executable.
            The process is directly invoked and not through a system shell.
        """
        from subprocess import Popen, PIPE
        argv = map_as_list(str, argv)
        popen_opts['stdout'] = popen_opts['stderr'] = PIPE
        proc = Popen([str(self)] + argv, **popen_opts)
        stdout, stderr = proc.communicate()
        ret = proc.wait()
        if py.builtin._isbytes(stdout):
            stdout = py.builtin._totext(stdout, sys.getdefaultencoding())
        if ret != 0:
            if py.builtin._isbytes(stderr):
                stderr = py.builtin._totext(stderr, sys.getdefaultencoding())
            raise py.process.cmdexec.Error(ret, ret, str(self),
                                           stdout, stderr,)
        return stdout

def _svn(self, cmd, *args):
        l = ['svn %s' % cmd]
        args = [self._escape(item) for item in args]
        l.extend(args)
        l.append('"%s"' % self._escape(self.strpath))
        # try fixing the locale because we can't otherwise parse
        string = fixlocale() + " ".join(l)
        try:
            try:
                key = 'LC_MESSAGES'
                hold = os.environ.get(key)
                os.environ[key] = 'C'
                out = py.process.cmdexec(string)
            finally:
                if hold:
                    os.environ[key] = hold
                else:
                    del os.environ[key]
        except py.process.cmdexec.Error:
            e = sys.exc_info()[1]
            strerr = e.err.lower()
            if strerr.find('not found') != -1:
                raise py.error.ENOENT(self)
            elif strerr.find("E200009:") != -1:
                raise py.error.ENOENT(self)
            if (strerr.find('file exists') != -1 or
                strerr.find('file already exists') != -1 or
                strerr.find('w150002:') != -1 or
                strerr.find("can't create directory") != -1):

def info_versions(self):
        versions = ['tox-%s' % tox.__version__]
        try:
            version = py.process.cmdexec("virtualenv --version")
        except py.process.cmdexec.Error:
            versions.append("virtualenv-1.9.1 (vendored)")
        else:
            versions.append("virtualenv-%s" % version.strip())
        self.report.keyvalue("tool-versions:", " ".join(versions))