Inconsistent error message in Python?

old_class_pow.py

# New style class
class B(object):
    def __init__(self, n):
        self._n = n

c = B(3)
d = B(4)

try:
    print(pow(c, d))
except Exception as e:
    print type(e), e.message

try:
    print(pow(c, d, d))
except Exception as e:
    print type(e), e.message

# will out put:
# <type 'exceptions.TypeError'> unsupported operand type(s) for ** or pow(): 'B' and 'B'
# <type 'exceptions.TypeError'> unsupported operand type(s) for pow(): 'B', 'B', 'B'

# Change it to old style class
class B:
    def __init__(self, n):
        self._n = n

c = B(3)
d = B(4)

try:
    print(pow(c, d))
except Exception as e:
    print type(e), e.message

try:
    print(pow(c, d, d))
except Exception as e:
    print type(e), e.message

# will out put:
# <type 'exceptions.TypeError'> unsupported operand type(s) for ** or pow(): 'instance' and 'instance'
# <type 'exceptions.AttributeError'> B instance has no attribute '__pow__'