lots of similar classes?

boncelet boncelet at udel.edu
Tue Jan 21 17:08:32 CET 2003

Thanks to all who responded.  I suspected there were better ways and
now I have several to try out.

Let me summarize the ideas:

1. from Duncan Booth:

>class A(Super):
>    def __init__(self, name='a', **args):
>        Super.__init__(self, name, **args)

I thought of this one shortly after I sent me inital message.  This is
part of what I'm currently using.  I originally wanted the user to be
able to specify the most common args by position, but realized that is
error-prone as well.

2. from Beni Cherniavsky:

> Besides using ``**kwargs``, if the only difference is the default value of
> `name`, consider getting it from a class attribute (set in each subclass)
> and not overriding __init__ at all.

The class attribute idea is very helpful for me.  This seems to be
best for all my subclasses (maybe 30-50 of them).  I can write a
generic super class and use class attributes to differentiate between
the subclasses.

3. from Mike Fletcher:
> With Python 2.2.x, this will work:

> class X(object):
>     def __init__( self, name='blah', y=2,z=3,m=4):

> class Y( X ):
>     def __init__( self, name='haha', *args, **named ):
>         super( Y, self).__init__( name, *args, **named )

I didn't know this worked.  Will have to try it out.  This is cool.

4. Roberto Cavada gave a suggestion that is above me.  Sorry.

5. Hans Nowak suggests using an "options class".  Very neat idea, also
one I have to test.

Thanks to all,

   Charlie Boncelet

Hans Nowak <wurmy at earthlink.net> wrote in message news:<3E2C2F7B.8070606 at earthlink.net>...
> boncelet wrote:
> > Pseudo-code looks like this:
> > 
> > class Super:
> >   def __init__(self,name,lots_of_other_arguments):
> >     self.name=name
> >     <<set rest of arguments, etc>>
> > 
> > class A(Super):
> >   def __init__(self,name='a',lots_of_other_arguments):
> >     Super.__init__(self,name,lots_of_other_arguments)
> >
> > My problem is rewriting the "lot_of_other_arguments" over and over
> > again seems wasteful, error-prone, and fragile.  Is there a better
> > way?
> To take a page from Martin Fowler's book, lots of arguments for a method is a 
> "code smell".  Consider writing a separate class for this.  I regularly use a 
> variant of the following, especially when command line options translate to 
> options in a class:
> class Options:
>      def __init__(self):
>          self.foo = ""
>          self.bar = None
>          # ...etc...
> options = Options()
> # set some options
> options.baz = "bletch"
> class MyClass:
>      def __init__(self, name, options):
>          self.options = options
> myclass = MyClass("foo", options)
> Now, your class uses an instance of Options to hold all these variables, rather 
> than having them in its own namespace.  Much easier to pass around.
> HTH,

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