Printing names of variables passed to a function

Question

In some circumstances, I want to print debug-style output like this:

# module test.py
def f()
  a = 5
  b = 8
  debug(a, b) # line 18

I want the debug function to print the following:

debug info at test.py: 18
function f
a = 5
b = 8

I am thinking it should be possible by using inspect module to locate the stack frame, then finding the appropriate line, looking up the source code in that line, getting the names of the arguments from there. The function name can be obtained by moving one stack frame up. (The values of the arguments is easy to obtain: they are passed directly to the function debug.)

Am I on the right track? Is there any recipe I can refer to?

Answer 1

You could do something along the following lines:

import inspect

def debug(**kwargs):
  st = inspect.stack()[1]
  print '%s:%d %s()' % (st[1], st[2], st[3])
  for k, v in kwargs.items():
    print '%s = %s' % (k, v)

def f():
  a = 5
  b = 8
  debug(a=a, b=b) # line 12

f()

This prints out:

test.py:12 f()
a = 5
b = 8

Answer 2

You're generally doing it right, though it would be easier to use AOP for this kinds of tasks. Basically, instead of calling "debug" every time with every variable, you could just decorate the code with aspects which do certain things upon certain events, like upon entering the function to print passed variables and it's name.

Please refer to this site and old so post for more info.