Exceptions are classes

The statement

raise Class, instance

is a shorthand for:

raise instance   # shorthand for raise instance.__class__, instance

#!/usr/bin/env python
class B(object):
    pass
class C(B):
    pass
class D(C):
    pass

for c in [B, C, D]:
    try:
        raise c()
    except D:
        print( "D")
    except C:
        print( "C")
    except B:
        print( "B")
print( " done ")

Note that the section 15.6.7 gives an example of how to catch exceptions in PyTango.