mathrick@hatsumi:/tmp$ cat tabs.py 
def foo():
	print "tabs"
        print "spaces"
foo()
mathrick@hatsumi:/tmp$ python tabs.py 
tabs
spaces
mathrick@hatsumi:/tmp$ python -tt tabs.py 
  File "tabs.py", line 3
    print "spaces"
                 ^
TabError: inconsistent use of tabs and spaces in indentation
mathrick@hatsumi:/tmp$