Re: Deciding inheritance at instantiation?

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From	Nobody <nobody@nowhere.com>
Subject	Re: Deciding inheritance at instantiation?
Date	Sat, 04 Aug 2012 00:52:53 +0100
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On Fri, 03 Aug 2012 13:48:08 -0700, Tobiah wrote:

> I have a bunch of classes from another library (the html helpers
> from web2py).  There are certain methods that I'd like to add to
> every one of them.  So I'd like to put those methods in a class,
> and pass the parent at the time of instantiation.  Web2py has
> a FORM class for instance.  I'd like to go:
> 
> 	my_element = html_factory(FORM)
> 
> Then my_element would be an instance of my class, and also
> a child of FORM.

You can use type() to create classes dynamically. E.g.:

	class my_base_class(object):
	    # extra methods

	subclasses = {}

	def html_factory(cls, *args, **kwargs):
	    name = "my_" + cls.__name__
	    if name not in subclasses:
	        subclasses[name] = type(name, (cls, my_base_class), {})
	    return subclasses[name](*args, **kwargs)

Thread

Deciding inheritance at instantiation? Tobiah <toby@tobiah.org> - 2012-08-03 13:48 -0700
  Re: Deciding inheritance at instantiation? Terry Reedy <tjreedy@udel.edu> - 2012-08-03 17:55 -0400
    Re: Deciding inheritance at instantiation? Tobiah <toby@tobiah.org> - 2012-08-06 10:42 -0700
  Re: Deciding inheritance at instantiation? Nobody <nobody@nowhere.com> - 2012-08-04 00:52 +0100
  Re: Deciding inheritance at instantiation? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-04 01:14 +0000
  Re: Deciding inheritance at instantiation? "Steven W. Orr" <steveo@syslang.net> - 2012-08-03 23:14 -0400
  Re: Deciding inheritance at instantiation? alex23 <wuwei23@gmail.com> - 2012-08-06 19:53 -0700
    Re: Deciding inheritance at instantiation? Tobiah <toby@tobiah.org> - 2012-08-07 10:52 -0700

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