Python: some newbie questions on sys.stderr and using function as argument

Question

I'm just starting on Python and maybe I'm worrying too much too soon, but anyways...

log = "/tmp/trefnoc.log"

def logThis (text, display=""):
    msg = str(now.strftime("%Y-%m-%d %H:%M")) + " TREfNOC: " + text
    if display != None:
        print msg + display
    logfile = open(log, "a")
    logfile.write(msg + "\n")
    logfile.close()
    return msg

def logThisAndExit (text, display=""):
    msg = logThis(text, display=None)
    sys.exit(msg + display)

That is working, but I don't like how it looks. Is there a better way to write this (maybe with just 1 function) and is there any other thing I should be concerned under exiting?

---

Now to some background...

Sometimes I will call logThis just to log and display. Other times I want to call it and exit. Initially I was doing this:

logThis ("ERROR. EXITING")
sys.exit()

Then I figured that wouldn't properly set the stderr, thus the current code shown on the top.

My first idea was actually passing "sys.exit" as an argument, and defining just logThis ("ERROR. EXITING", call=sys.exit) defined as following (showing just the relevant differenced part):

def logThis (text, display="", call=print):
    msg = str(now.strftime("%Y-%m-%d %H:%M")) + " TREfNOC: " + text
    call msg + display

But that obviously didn't work. I think Python doesn't store functions inside variables. I couldn't (quickly) find anywhere if Python can have variables taking functions or not! Maybe using an eval function? I really always try to avoid them, tho. Sure I thought of using if instead of another def, but that wouldn't be any better or worst.

Anyway, any thoughts?

Answer 1

You could modify logThis to take a final argument called shouldExit which defaults to None, then as a final step in that method, if the value is true then call sys.exit.

Answer 2

There's no reason for "logThisAndExit", it doesn't save you much typing over

sys.exit(logThis(text)+display)

(compare logThisAndExit(text, display))

or

sys.exit(logThis(text))

(compare logThisAndExit(text))

Not that I'm entirely sure why you like your exit messages formatted as log lines.

In answer to your original question: you're missing parentheses: call(msg+display) works fine. But I think that's waaaay overengineering for logging/exiting stuff. Anyone who maintains your code will have to understand your function to know when it's exiting and when it's not.

Answer 3

print is a keyword, not a function, in python < 3. try this:

def do_print(x):
    print x

def logThis (text, display="", call=do_print):
    msg = str(now.strftime("%Y-%m-%d %H:%M")) + " TREfNOC: " + text
    call(msg + display)

Is there any reason you don't use the logging module? (see http://onlamp.com/pub/a/python/2005/06/02/logging.html)

Answer 4

Just as reference, this is my final code after assimilating hints from David and moshez. In the end I decided I wanted just 1 function for now. Thanks everyone!

log = "/tmp/trefnoc.log"

def logThis (text, display=""):
    msg = str(now.strftime("%Y-%m-%d %H:%M")) + " TREfNOC: " + text
    if display != None:
        print msg + display
    logfile = open(log, "a")
    logfile.write(msg + "\n")
    logfile.close()
    return msg

# how to call it on exit:
sys.exit(logThis("ERROR, EXITING", display=None))

Answer 5

For logging, it is probably easier to use the logging module.

For exiting, if you have any error, use:

sys.exit(1)

and if there is no error, either just let the script run out of statements or:

sys.exit(0)