$ python2
Python 2.7.5 (default, Jun 25 2014, 10:19:55) 
[GCC 4.8.2 20131212 (Red Hat 4.8.2-7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> def foo(s):
...     if isinstance(s, str):
...         print(s)
...         return
...     raise TypeError, 'unexpected type "%s"' % repr(s)
... 
>>> 

$ python3
Python 3.3.2 (default, Jun 30 2014, 17:20:03) 
[GCC 4.8.3 20140624 (Red Hat 4.8.3-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def foo(s):
...     if isinstance(s, str):
...         print(s)
...         return
...     raise TypeError, 'unexpected type "%s"' % repr(s)
  File "<stdin>", line 5
    raise TypeError, 'unexpected type "%s"' % repr(s)
                   ^
SyntaxError: invalid syntax
>>>