To get the output of ls, use stdout=subprocess.PIPE.

>>> proc = subprocess.Popen('ls', stdout=subprocess.PIPE)
>>> output = proc.stdout.read()
>>> print output
bar
baz
foo

The command cdrecord --help outputs to stderr, so you need to pipe that indstead. You should also break up the command into a list of tokens as I've done below, or the alternative is to pass the shell=True argument but this fires up a fully-blown shell which can be dangerous if you don't control the contents of the command string.

>>> proc = subprocess.Popen(['cdrecord', '--help'], stderr=subprocess.PIPE)
>>> output = proc.stderr.read()
>>> print output
Usage: wodim [options] track1...trackn
Options:
    -version    print version information and exit
    dev=target  SCSI target to use as CD/DVD-Recorder
    gracetime=# set the grace time before starting to write to #.
...

If you have a command that outputs to both stdout and stderr and you want to merge them, you can do that by piping stderr to stdout and then catching stdout.

subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)

As mentioned by Chris Morgan, you should be using proc.communicate() instead of proc.read().

>>> proc = subprocess.Popen(['cdrecord', '--help'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>> out, err = proc.communicate()
>>> print 'stdout:', out
stdout: 
>>> print 'stderr:', err
stderr:Usage: wodim [options] track1...trackn
Options:
    -version    print version information and exit
    dev=target  SCSI target to use as CD/DVD-Recorder
    gracetime=# set the grace time before starting to write to #.
...

You’ll need to use the stdout and/or stderr arguments. https://docs.python.org/3/library/subprocess.html#subprocess.run

Edit: link to #subprocess.run

This may help you:

def execute(cmd):
    popen = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE,
                             universal_newlines=True)
    for stdout_line in iter(popen.stdout.readline, ""):
         yield stdout_line
    popen.stdout.close()
    return_code = popen.wait()
    if return_code:
        raise subprocess.CalledProcessError(return_code, cmd)

So you can basically execute:

for line in execute("fping -l google.com"):
    print(line)

For example.

If you have Python version 2.7 or later, you can use subprocess.check_output which basically does exactly what you want (it returns standard output as a string).

A simple example (Linux version; see the note):

import subprocess

print subprocess.check_output(["ping", "-c", "1", "8.8.8.8"])

Note that the ping command is using the Linux notation (-c for count). If you try this on Windows, remember to change it to -n for the same result.

As commented below, you can find a more detailed explanation in this other answer.

If you're using 2.7, you can use subprocess.check_output():

>>> import subprocess
>>> output = subprocess.check_output(['echo', '640x360'])
>>> print output
640x360

If not:

>>> p = subprocess.Popen(['echo', '640x360'], stdout=subprocess.PIPE)
>>> p.communicate()
('640x360\n', None)