How to tell which subclass was used to instantiate object

[Frank Millman]

Hi all

I have a question regarding inheritance. I have come up with a
solution, but it is not very elegant - I am sure there is a more
pythonic approach. Assume the following class definitions.

class Table:
    def __init__(self,table_name,table_type):

class Master(Table):
    def __init__(self,table_name,table_type):
        Table.__init__(self,table_name,table_type)

class Transaction(Table):
    def __init__(self,table_name,table_type):
        Table.__init__(self,table_name,table_type)

class Armaster(Master):
    def __init__(self,table_name,table_type):
        Master.__init__(self,table_name,table_type)

Table is the main class, which represents a database table. Master is
a subclass that encapsulates various common characteristics of a
'master file' type of table. Transaction is a subclass that
encapsulates various common characteristics of a 'transaction file'
type of table. ArMaster is a subclass that is created to handle
specific requirements for the ArMaster table, which is a 'master file'
type of table.

Both of the following would be errors -

class Armaster(Table):
    def __init__(self,table_name,table_type):
        Table.__init__(self,table_name,table_type)

class Armaster(Transaction):
    def __init__(self,table_name,table_type):
        Transaction.__init__(self,table_name,table_type)

By inheriting from the incorrect class, the special methods to handle
a 'Master' type table have been bypassed. My question is, how can
Table check that objects have inherited from the correct subclasses?

Here is my inelegant solution. Assume that table_type contains the
string 'Master'.

class Master(Table):
    def __init__(self,table_name,table_type):
        self.my_type = 'Master'
        Table.__init__(self,table_name,table_type)

class Table:
    def __init__(self,table_name,table_type):
        if hasattr(self,'my_type'):
            ok = (self.my_type == table_type)
        else:
            ok = False
        if not ok:
            raise RuntimeError('%s must be of type %s' %
               (table_name,table_type))

Is there a more direct way for a top-level class to determine which
subclasses were used to instantiate it?

Thanks

Frank Millman