setTrace() in Python (redux)

Question

Apologies for reposting but I had to edit this question when I got to work and realized I needed to have an account to do so. So here it goes again (with a little more context).

I'm trying to time how long a script takes to execute, and I am thinking of doing that by checking the elapsed time after every line of code is executed. I've done this before when the script has contained method definitions, but am not sure how it would work in this instance.

So my question is: Is there a way to use the setTrace() function in a script that has no method definitions? i.e.

for i in range(1, 100):
    print i

def traceit(frame, event, arg):
    if event == "line":
        lineno = frame.f_lineno
        print "line", lineno

    return traceit

sys.settrace(traceit)

Answer 1

No, as the docs say, "The trace function is invoked (with event set to 'call') whenever a new local scope is entered" -- if you never enter a local scope (and only execute in global scope), the trace function will never be called. Note that settrace is too invasive anyway for the purpose of timing "how long a script takes to execute" as it will alter what it's measuring too much; if what you say is actually what you want, just take the time at start of execution and register with atexit a function that gets the time again and prints the difference. If what you want is different, i.e., profiling, see cProfile .

Further note that the code example you give couldn't possibly do anything useful (even though I've edited it to fix an indent error): first it loops, then it defs a function, finally it calls settrace... then immediately ends because there's no more code after that! If you want anything to happen before that loop start, and you want to have everything at module top level (bad idea, but, whatever), you have to put the "anything" lexically before the loop, not after...;-)