python exception inheritance

exceptions.py

class A(Exception):
    pass

class B(A):
    pass


try:
    raise B
except A:
    print 'raised B, excepted A'


try:
    raise A
except B:
    print 'raised A, catched B'

# output 

raised B, excepted A
Traceback (most recent call last):
  File "exceptions.py", line 15, in <module>
    raise A
__main__.A