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Dynamically print the Executing Line of Code?

JohnDye

Kind of an odd question and it may have implications that I'm not seeing, but I'm wondering if anyone knows of a little method to instruct python to print the executing line of code, either before or after it executes instead of inserting print statements, you know like...everywhere.

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Accepted answers

JasonScheirer

Isn't that what a debugger is for?

You could do this, but it's a terrible idea and will slow your program down by orders of magnitude:

import inspect import sys  def tracefunction(frame, event, arg):     if event == "line":         info = inspect.getframeinfo(frame)         fname, lineno, fn = info.filename, info.lineno, info.function         with open(fname, 'rb') as f:             line = [line.rstrip() for line in f][lineno - 1]             print "Function: {} (in file {}:{}) | {}".format(fname, fn, lineno, line)     return tracefunction  def registertracefunction():     sys.settrace(tracefunction)  registertracefunction()  def mainfunction():     for x in xrange(10):         print x * 5  if __name__ == "__main__":     mainfunction()

That is, paste the code up through registertracefunction() line to the top of your script and it will print out every line it's on.

All comments

TimBarnes

This may be completely obvious to you, apologies if it is, but when you are trying to debug a python addin, having the Geoprocessing> Python command line open in ArcMap while running the tool/button etc will show any error messages there.

JohnDye

Isn't that what a debugger is for?

You could do this, but it's a terrible idea and will slow your program down by orders of magnitude:

import inspect
import sys

def tracefunction(frame, event, arg):
    if event == "line":
        info = inspect.getframeinfo(frame)
        fname, lineno, fn = info.filename, info.lineno, info.function
        with open(fname, 'rb') as f:
            line = [line.rstrip() for line in f][lineno - 1]
            print "Function: {} (in file {}:{}) | {}".format(fname, fn, lineno, line)
    return tracefunction

def registertracefunction():
    sys.settrace(tracefunction)

registertracefunction()

def mainfunction():
    for x in xrange(10):
        print x * 5

if __name__ == "__main__":
    mainfunction()

That is, paste the code up through registertracefunction() line to the top of your script and it will print out every line it's on.

Thanks Jason,
I figured that something like this would degrade performance. Debugging would be a good option except Python Addins don't lend themselves to debugging quite as well as something like a Script tool and I was really hoping to not have to resort to inserting print statements on every other line.

MathewCoyle

The best option I know of is using trace. It will can create a file of the code executed. Here is an example.

http://pymotw.com/2/trace/

Profile also has some good options.

http://docs.python.org/2/library/profile.html

JasonScheirer

Isn't that what a debugger is for?

You could do this, but it's a terrible idea and will slow your program down by orders of magnitude:

import inspect import sys  def tracefunction(frame, event, arg):     if event == "line":         info = inspect.getframeinfo(frame)         fname, lineno, fn = info.filename, info.lineno, info.function         with open(fname, 'rb') as f:             line = [line.rstrip() for line in f][lineno - 1]             print "Function: {} (in file {}:{}) | {}".format(fname, fn, lineno, line)     return tracefunction  def registertracefunction():     sys.settrace(tracefunction)  registertracefunction()  def mainfunction():     for x in xrange(10):         print x * 5  if __name__ == "__main__":     mainfunction()

That is, paste the code up through registertracefunction() line to the top of your script and it will print out every line it's on.

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