design question: no new attributes

[Ben Finney]

"Alan Isaac" <aisaac at american.edu> writes:

> "Ben Finney" <bignose+hates-spam at benfinney.id.au> wrote:
> > The Pythonic design is: don't expect to have such control over
> > users of your code.
>
> I know this is a popular response, but the fact of the matter
> remains that it can be helpful to know when someone tries to set a
> value for a nonexisting attribute.

That's quite a different request from your original request asking the
Pythonic design for *preventing* setting of new attributes.

> This is especially true if there have been any interface changes.

If the interface has changed, then you don't need to trap *every*
setting of an attribute; only the names that you know have changed.

===== foo_v1.py =====

class Foo(object):
    def bar(self):
        return 17

    spam = 42
=====

===== foo_v2.py =====

import logging

class Foo(object):
    def baz(self):
        return 13

    eggs = 69

    def bar(self):
        """ Obsolete interface for Foo.baz() """
        logging.warn("Deprecated Foo.bar() call, please use Foo.baz()")
        return self.baz()

    def _get_spam(self):
        """ Obsolete interface for Foo.eggs """
        logging.warn("Deprecated Foo.spam reference, please use Foo.eggs")
        return self.eggs
    def _set_spam(self, value):
        """ Obsolete interface for Foo.eggs """
        logging.warn("Deprecated Foo.spam reference, please use Foo.eggs")
        self.eggs = value
    spam = property(_get_spam, _set_spam)
=====

After a reasonable grace period, you can drop these compatibility
interfaces in a future version.

-- 
 \     "For every complex problem, there is a solution that is simple, |
  `\                            neat, and wrong."  -- Henry L. Mencken |
_o__)                                                                  |
Ben Finney