[Tutor] yet another question on OO inheritance

[Kent Johnson]

On Tue, Aug 18, 2009 at 1:47 PM, Serdar Tumgoren<zstumgoren at gmail.com> wrote:
> Hi all,
>
> I've hit another gray area for an application I'm working on.
> Specifically, I have a campaign Committee object, and then subclasses
> called CandidateCommittee and PresidentialCommittee. Depending on the
> type of committee, I have to execute a series of SQL statements to
> pull data (used to populate instance attributes of each committee
> type).
>
> Several of these queries are identical, except for the table names
> from which I'm pulling the data:

> So I'm thinking I could reduce code duplication by moving the SQL
> queries to the Committee object:
>
> Committee(object):...
>
>    def get_data(self):
>        sql = """
>        select id, name
>        from table_'%(tablename)s'
>        """ % {'tablename':name}
>
> CandidateCommittee(Committee):...
>    def __init__(self):
>        super(CandidateCommittee, self).__init()
>
> PresidentialCommittee(Committee):
>    def __init__(self):
>        super(PresidentialCommittee, self).__init()
>
> But if I do this, how would I set the "name" variable inside the
> "get_data" method when I instantiate one of the subclasses?

A nice way to do this is with a class attribute. For example:
class Committee(object):

   def get_data(self):
       sql = """
       select id, name
       from table_'%(tablename)s'
       """ % {'tablename':self.tablename}

class CandidateCommittee(Committee):
   tablename = 'CandidateTable'

PresidentialCommittee(Committee):
   tablename = 'PresidentialTable'

When you call Committee.get_data() it will get tablename from the
class of the instance being used.

Kent