TypeError:exceptions must be old-style classes or derived from BaseException, not str

Question

The sole argument to raise indicates the exception to be raised. This must be either an exception instance or an exception class (a class that derives from Exception).

Try this:

test = 'abc'
if True:
    raise Exception(test + 'def')

You can't raise a str. Only Exceptions can be raised.

So, you're better off constructing an exception with that string and raising that. For example, you could do:

test = 'abc'
if True:
    raise Exception(test + 'def')

OR

test = 'abc'
if True:
    raise ValueError(test + 'def')

Hope that helps

It should be an exception.

You want to do something like:

raise RuntimeError(test + 'def')

In Python 2.5 and below, your code would work, as then it was allowed to raise strings as exceptions. This was a very bad decision, and so removed in 2.6.