sys.settrace example

>>> import sys
>>> def stuff():
...     print("calling stuff!")
... 
>>> def printer(frame, event, arg):
...     print(frame, event, arg)
...     return printer  # return itself to keep tracing
... 
>>> sys.settrace(printer)  # register the tracing function
>>> stuff()
(<frame object at 0x10d3625c0>, 'call', None)
(<frame object at 0x10d3625c0>, 'line', None)
(<frame object at 0x10d3625c0>, 'return', (u'stuff()\n', 8))
(<frame object at 0x10d259050>, 'call', None)
(<frame object at 0x10d259050>, 'line', None)
(<frame object at 0x10d259898>, 'call', None)
(<frame object at 0x10d259898>, 'line', None)
calling stuff!
(<frame object at 0x10d259898>, 'return', None)
(<frame object at 0x10d259050>, 'return', None)
>>> sys.settrace(None)  # turn it off
(<frame object at 0x10d3625c0>, 'call', None)
(<frame object at 0x10d3625c0>, 'line', None)
(<frame object at 0x10d3625c0>, 'return', (u'sys.settrace(None)  # turn it off\n', 34))
(<frame object at 0x10d351a70>, 'call', None)
(<frame object at 0x10d351a70>, 'line', None)
>>> print('hi') # tracing is done
hi