Python 3.4.3 subprocess.Popen get output of command without piping?

Question

I am trying to assign the output of a command to a variable without the command thinking that it is being piped. The reason for this is that the command in question gives unform

Answer 1

Yes, you can use the pty module.

>>> import subprocess
>>> p = subprocess.Popen(["ls", "--color=auto"], stdout=subprocess.PIPE)
>>> p.communicate()[0]
# Output does not appear in colour

With pty:

import subprocess
import pty
import os

master, slave = pty.openpty()
p = subprocess.Popen(["ls", "--color=auto"], stdout=slave)
p.communicate()
print(os.read(master, 100)) # Print 100 bytes
# Prints with colour formatting info

Note from the docs:

Because pseudo-terminal handling is highly platform dependent, there is code to do it only for Linux. (The Linux code is supposed to work on other platforms, but hasn’t been tested yet.)

A less than beautiful way of reading the whole output to the end in one go:

def num_bytes_readable(fd):
    import array
    import fcntl
    import termios
    buf = array.array('i', [0])
    if fcntl.ioctl(fd, termios.FIONREAD, buf, 1) == -1:
        raise Exception("We really should have had data")
    return buf[0]

print(os.read(master, num_bytes_readable(master)))

Edit: nicer way of getting the content at once thanks to @Antti Haapala:

os.close(slave)
f = os.fdopen(master)
print(f.read())

Edit: people are right to point out that this will deadlock if the process generates a large output, so @Antti Haapala's answer is better.