Using class attributes

[Leo Breebaart]

Arnaud Delobelle <arnodel at googlemail.com> writes:

> Descriptors to the rescue :)
> 
> def read_body_from(filename):
>     print "** loading content **"
>     return "<content of '%s'>" % filename
> 
> # This is a kind of class property
> class TemplateFilename(object):
>     def __get__(self, obj, cls):
>         return "%s.tmpl" % cls.__name__
> 
> # And this is a kind of cached class property
> class TemplateBody(object):
>     def __get__(self, obj, cls):
>         try:
>             return cls._body
>         except AttributeError:
>             cls._body = read_body_from(cls.template_filename)
>             return cls._body
> 
> class Foo(object):
>     template_filename = TemplateFilename()
>     template_body = TemplateBody()
> 
> class FooA(Foo):
>    pass
> 
> class FooB(Foo):
>    pass

Very enlightening, thanks!

By the way, I completely agree with the other posters in this
thread that intricate solutions such as this are likely to be
overkill, especially since at this point I have no idea if the
inefficiency of reading those templates multiple times would at
all matter (frankly, I'd doubt it). But it's certainly been
educational to learn about these techniques.

One observation: if I implement the descriptor solution as given
above, the code works perfectly, but running the code through
pychecker now causes an error, because that again causes an
attempt to read from the non-existant base class template file
"Foo.tmpl"...

-- 
Leo Breebaart  <leo at lspace.org>