How to log errors in python when using the os module

Question

I'm trying to incorporate a simple way to keep track of a periodic mysqldump command I want to run using the os module in python. I've written this, but in testing it doesn't raise the exception, even when the mysqldump command completes with an error. I'm pretty new to python, so I might be approaching this terribly, but I thought I would try to get pointed in the right direction.

db_dump = "mysqldump -u %s -p%s --socket=source_socket --databases %s | mysql -u %s -p%s   --socket=dest_socket" % (db_user, db_pass, ' '.join(db_list), db_user, db_pass)

try:
    os.system(db_dump)
except:
    logging.error("databases did not dump")
else:    
    logging.info("database dump complete")

Answer 1

os.system is not a very robust or powerful way to call system commands, I'd recommend using subprocess.check_output() or subprocess.check_call

ie,

>>> cmd = 'ls -l'
>>> badcmd = 'ls /foobar'
>>> subprocess.check_call(cmd.split())
0
>>> subprocess.check_call(badcmd.split())
ls: /foobar: No such file or directory
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 511, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['ls', '/foobar']' returned non-zero exit status 1