python - Save output of os.system to text file

Question

I'm not great on all the technical terms so I'll do my best to explain my problem.

I've written a small script to open android SDK and check for attached devices (using windows 10 and python 2.7.14). The code I've got is as follows:

import os
import datetime
import time

print 'Current Directory:', os.getcwd()
print 'Opening Android SDK...'
os.chdir('C:\android-sdk\platform-tools')
print 'Current Directory:', os.getcwd()
t = time.ctime()
print t
print 'Checking for connected devices:'
os.system('adb devices -l')

That all works fine, but I want to get the last 3 lines to save to a text file. I've tried f = open('logfile.txt', 'w') then converting it all to a string using s = str(t, 'Checking for connected devices:', os.system('adb devices -l')) and writing it to the file and closing it, but it's not working. It's not even creating the file, let alone writing anything to it.

I'm probably missing something key but I'm a newbie at this so please be nice!

Any help would be much appreciated.

Many thanks

Edit: whole code with the write stuff included:

import os
import datetime
import time

print 'Current Directory:', os.getcwd()
print 'Opening Android SDK...'
os.chdir('C:\android-sdk\platform-tools')
print 'Current Directory:', os.getcwd()
t = time.ctime()
f = open('logfile.txt', 'w')
s = str(t, 'Checking for connected devices:', os.system('adb devices -l'))
f.write(s)
f.close()

Answer 1

os.system executes the command in a subshell and returns the command's exit code. It does not provide any mean to capture the outputs of the command ("outputs" => what the command prints to it's stdout/stderr streams).

To capture the command's outputs you'll have to use some of the subprocess module's feature, the most obvious here being subprocess.check_output

# ...
import subprocess
# ...
# NB : you may want to catch subprocess.CalledProcessError here
out = subprocess.check_output(['adb',  'devices', '-l'])
msg = "{t}
Checking for connected devices:
{out}".format(t=t, out=out)
with open('logfile.txt', 'w') as f:
    f.write(msg)