Python, can't get assert_raises to work properly

Question

I am currently doing the "Learn Python the Hard Way" of Zed A. Shaw and I am having quite a bit of trouble with exercice 49 using assert_raises. Here is the code that I am using in my test file:

def test_parseVerb():
    assert_raises("ParserError",parser.parse_verb,[('stop', 'the'),
                                                   ('noun', 'bear')])

And this is the error that PowerShell is giving me:

======================================================================
ERROR: tests.parser_tests.test_parseVerb
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\MrnMicro\Python27\lib\site-packages\nose\case.py", line 197, in runTest
    self.test(*self.arg)
  File "C:\Documents and Settings\sthma2\Documents\LPTHW\Projects\ex48\tests\parser_tests.py", line 37, in test_parseVer
b
    assert_raises("ParserError",parser.parse_verb,fail_list)
  File "C:\MrnMicro\Python27\lib\unittest\case.py", line 476, in assertRaises
    callableObj(*args, **kwargs)
  File "C:\MrnMicro\Python27\lib\unittest\case.py", line 117, in __exit__
    if not issubclass(exc_type, self.expected):
TypeError: issubclass() arg 2 must be a class or tuple of classes

----------------------------------------------------------------------
Ran 10 tests in 0.016s

FAILED (errors=1)

I have no idea what is going on to be honest, if someone could help it would be much appreciated !

Thanks !

EDIT

def parse_verb(word_list):
    skip(word_list, 'stop')

    if peek(word_list) == 'verb':
        return match(word_list, 'verb')
    else:
        raise ParserError("Expected a verb next.")

Answer 1

You need to provide the actual class of the exception as first parameter, not a string containing the name, e.g.

assert_raises(ZeroDivisionError, operator.div,  1, 0)

The documentation is actually in the standard module unittest, nose adapts the names to pep8.