Issue with python subprocess

Question

I'm having some trouble with some code I'm working on. It should be obvious as to what it does in the code. Here is the python code I have:

import RPi.GPIO as gpio
import subprocess
gpio.setmode(gpio.BCM)
gpio.setup(18, gpio.IN, pull_up_down=gpio.PUD_UP)
gpio.setup(2, gpio.OUT)
p2on = False
while True:
    input_state = gpio.input(18)
    if input_state == False:
        if p2on == False:
            subprocess.call(['say','The light is on'])
            p2on = True
        else:
            subprocess.call(['say','The light is off'])
            p2on = False
    if p2on == True:
        gpio.output(2, True)
    else:
        gpio.output(2, False)

The say command I have thrown in there is just an alias I setup for basic TTS. The say command works on it's own, and I have two .sh scripts that call those same say commands, the code works. However, when I try just calling the command directly as above instead of:

import os
os.system('sh /home/pi/on.sh')

I get an error. The os.system method works, but only if I call another script file, and that's just too messy. The error that I get is:

Traceback (most recent call last):
  File "button.py", line 13, in <module>
    subprocess.call(['say','The light is on'])
  File "/usr/lib/python2.7/subprocess.py", line 493, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/usr/lib/python2.7/subprocess.py", line 679, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1259, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

Any ideas?

Answer 1

Aliases are something your shell interprets and runs. It's not a system call. That's why it works from your .sh scripts, but not this python script.

I would suggest changing your call to:

subprocess.call(['/bin/sh', '-i', '-c', 'say', 'the light is ...')