sys.settrace usage sample

settrace.py

import sys
import inspect


class Tracer(object):
    def __init__(self):
        self._indentation_level = 0
        
    @property
    def indentation_level(self):
        return self._indentation_level
    
    @indentation_level.setter
    def indentation_level(self, value):
        self._indentation_level = max(0, value)
        
    def __enter__(self):
        sys.settrace(self)
        
    def __exit__(self, exc_type, exc_value, traceback):
        sys.settrace(None)
        
    def __call__(self, frame, event, args):
        frameinfo = inspect.getframeinfo(frame)
        filename = frameinfo.filename
        
        # Use `in` instead of comparing because you need to cover for `.pyc` files as well.
        if filename in __file__:
            return None
        
        if event == 'return':
            self.indentation_level -= 1
        elif event == 'call':
            print "{}{}{}".format("  " * self.indentation_level,
                                  frameinfo.function,
                                  inspect.formatargvalues(*inspect.getargvalues(frame)))
            self.indentation_level += 1
        else:
            return None
            
        return self