A simple Python debugging function

By Vasudev Ram

[ Update: I do know about Python's logging module but felt it was overkill for my current needs, and also wanted more flexibility. ]

[ Update 2: Made some minor improvement to the code for better output. You can now print a debug message without any associated values. ]

I just whipped up this simple debugging function to help me debug my Python programs:

# vr_debug.py

# Debug utility functions by VR.
# Author: Vasudev Ram - http://www.dancingbison.com
# Description: Simple utility functions for debugging Python programs.

import sys
import os

def vr_debug(message, *values):
    vr_debugging = os.getenv("VR_DEBUG")
    if vr_debugging is None:
        # Debugging is off, do nothing.
        return
    if len(values) == 0:
        print message,
    else:
        print message, ":", 
    #print "len(values):", len(values)
    for value in values:
        #print repr(value), " ",
        print repr(value),
    print

def main():
    # Test the vr_debug function with some calls.
    vr_debug('z') # Debug message without any associated values.
    # Debug messages with values:
    vr_debug('a', 1)
    vr_debug('b', 1, "hi")
    vr_debug('c', 1, "hi", True)
    vr_debug('d', 1, "hi", True, [2, 3])
    vr_debug('d', 1, "hi", True, [2, 3], {'a': 'apple', 'b': 'banana'})

if __name__ == '__main__':
    main()

# EOF

To use the vr_debug function (as shown in the above program), you have to set an environment variable VR_DEBUG to some non-null value, say 1:

C:\>set VR_DEBUG=1

Then you can run the program to test the debug function, with:

C:\>python vr_debug.py

Here is its output:

z
a : 1
b : 1 'hi'
c : 1 'hi' True
d : 1 'hi' True [2, 3]
d : 1 'hi' True [2, 3] {'a': 'apple', 'b': 'banana'}

To turn off debugging, just set VR_DEBUG to a null value:

C:\>set VR_DEBUG=

Note: The above environment variable settings were for Windows. For Linux/UNIX, using bash, you would do this:

$ export VR_DEBUG=1

to set the environment variable, but the unset command to unset it:

$ unset VR_DEBUG

The above program included both the vr_debug function and a few tests of it. To use the vr_debug function in your own code, just copy the file vr_debug.py to somewhere on your PYTHONPATH and then import it into any Python files in which you want to use it:

from vr_debug import vr_debug

Now you can call it just as in the above program.

This is just a simple debug function, improvements are possible, such as passing an output destination argument, with a default of sys.stderr (so that output is un-buffered, unlike with the print command), and also so that a different destination can be given, such as a file opened for writing. To do that, you would have to change all the print statements to something like:

out_fil.write(...)

, and add

out_fil=sys.stderr

as another argument to the vr_debug function.

I've written a few different variations of such debugging functions over the years, in Python as well as other languages, but have somehow never seemed to arrive at a solution that satisfies me.

On the other hand, there is something to be said for KISS ...

For another Python debugging technique, see my earlier post:

Using sys._current_frames() and the Python traceback module for debugging

- Vasudev Ram - Dancing Bison Enterprises

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