Playing mp3 from variable

[mstone326]

Very much a beginner and just messing around having fun with Python. I'm working on a Raspberry Pi with Raspbian.

I put together the code below on Python 3. The song will not play when I put the bolded play_sound (seen below). However, if I replace the bolded play_sound with the actual song name, os.system('mpg123 -q song1.mp3 &') that song will play just fine just not when I replace that with the variable play_sound.

Can anyone nudge me in the right direction? The random.choice correctly chooses and prints a song from the list, but the next line won't play. Thank you in advance.

from gpiozero import LED, Button
import os
import random
led = LED(17)
btn = Button(4)
songs = ['song1.mp3', 'song2.mp3', 'song3.mp3']


while True:
    btn.wait_for_press()
    btn.wait_for_release()
    play_sound = random.choice(songs)
    print (play_sound)    [i]#so I know random.choice is working properly[/i]
    os.system('mpg123 -q  [b]play_sound[/b]  &')
    led.on()
    btn.wait_for_press()
    btn.wait_for_release()
    led.off()